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NBSIR 82-2503

Development of An Ease of

Ignition Test Using A Flame

Exposure

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

June 1 982

Supported in part by:

Naval Sea Systems Command

Washington, DC

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NBSIR 82-2503

DEVELOPMENT OF AN EASE OF

IGNITION TEST USING A FLAME

EXPOSURE

J. R. Lawson and W. J. Parker

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Washington, DC 20234

June 1 982

Supported in part by:

Naval Sea Systems Command

Washington, DC

and

Gypsum Association

Evanston, IL

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

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

Page

List of Figures iv

List of Tables v

Abstract 1

1. Introduction 2

2. Test Parameters ^

2.1 Specimen Size ^ 2.2 Specimen Conditioning ^ 2.3 Spacing Between Specimens ^ 2.4 Ventilation ^ 2.5 Cooling Blocks

2.6 Gas Supply 10

2.6.1 Type of Gas 10

2.6.2 Incident Heat Flux versus Gas Flow Rate 12

2.6.3 Flame Attachment Time versus Total Heat Flux. . . 13

3. Ignition Criteria 14

3.1 Flame Attachment 14

3.2 Fuel Contribution 15

4. Ignition Data on Materials 17

5. Comparison with Full-Scale Tests 17

6. Precision and Accuracy 21

7 . Summary 22

8. Acknowledgment 24

9. References 25

APPENDIX A Ignition Test Apparatus

APPENDIX B Copper Disk Calorimeter

iii
LIST OF FIGURES

Page

Figure I. Photograph of Ignition Test Apparatus 26

Figure 2. Sketch of Ignition Apparatus. . 27

Figure 3. Copper Disk Calorimeter 28

Figure 4. Total Incident Heat Flux Versus Gas Flow Rate 29

Figure 5. Incident Heat Flux Versus Time to Flame Attachment for

Wood Fiber Ceiling Board 30

Figure 6. Fuel Contribution Times for a Variety of Materials. . . 31

Figure 7 . Flame Attachment Times in Full-Scale Tests Versus

Flame Attachment Times in the Ease of Ignition Test . . 32

Figure 8. Drawing of Ease of Ignition Test Apparatus 33

Figure 9. Drawing of Specimen Frame and Cooling Block 34

Figure 10. Phototube and Time Marker Circuits 35

3 Figure 11. Phototube Record for 32 kg/m (2 PCF) Polyisocyanurate

Foam 36

Figure 12. Schematic Diagram of the Operation of the Copper Disk

Calorimeter 37

Figure 13. Drawing of the Copper Disk Calorimeter 38

Figure 14. Chart Record of the Incident Flux Measurement 39
LIST OF TABLES

Page

Table 1. Effect of Specimen Height AO

Table 2. Effect of Conditioning on the Ignition of Red Oak .... 41

Table 3. Comparison of Temperatures Produced by City Gas and

Methane in the Central Vertical Plane of the

Exposure Flame ^2

Table 4. Comparison of Incident Heat Fluxes for City Gas

and Methane ^3

Table 5. Times to Flame Attachment and Fuel Contribution

Table 6. Flame Attachment Times in the Ease of Ignition Test and

Full-Scale Room Fire Tests ^8

Table 7. Comparison of Ease of Ignition Results with Full-Scale

Room Fire Tests of Underwriters' Laboratories 50

Table 8. Precision-Tests with Standard Hardboard Specimens .... 51

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DEVELOPMENT OF AN EASE OF IGNITION

TEST USING A FLAME EXPOSURE

J. R. Lawson and W. J. Parker

Abstract

A test for the ease of ignition of interior finish

materials by flame exposure was developed. Two specimens,

140 mm (5.5 in) wide by 152 mm (6 in) high, face each

other at a distance of 53 mm (2.1 in) apart. A methane

diffusion flame bums between these surfaces and extends

to about 152 mm (6 in) above them. The operator observes

the specimen surface and records the time-to-flame attachment. A phototube, which views the exposure flame, shows

a marked increase in output when the specimens start contributing fuel. The ignition sensitivity is expressed by

the time-to-f lame attachment and by the time-to-fuel contribution. The times-to-f lame attachment measured in the

ignition apparatus generally ranked 22 materials with the

observed times of wall involvement in full-scale tests.

The results of this test may be useful as one factor in

computer models of fire growth in enclosures.

Key Words: Building materials; fire tests; flame

attachment; heat flux; ignition; room

fires; wall coverings

1
1. INTRODUCTION

The history of fire research dates back to man's early attempts to

understand fires which originated through natural events. The first

ignition studies may have revolved around the observation that dead, dry

grass and wood ignited easily whereas green, wet flora was difficult to

ignite. As knowledge and use of fire increased, building laws (such as

those in early Rome) reflected concern over the ignitability and combustibility of building materials. Crude tests were probably used to

evaluate materials for use in certain types of construction. Somewhat

more refined tests and observations are being made today.

The rate and extent of the fire buildup in an enclosure depends in

part on the time to ignition, rate of flame spread, rate of heat release,

potential heat, and thermal properties of the materials comprising the

wall, ceiling, and floor surfaces and the furnishings. The flame spread

rate of interior finish materials has traditionally been regulated

through the building codes by the ASTM E 84 tunnel test [1]^. For

materials with low flame spread indexes (FSI) , the tunnel rating is

based to a large extent on the maximum distance of flame travel and to

a lesser extent on when the specimen ignites or how rapidly the flame

spreads. However, a room lined with a low-density foamed plastic having

Figures in brackets indicate literature references at the end of this

paper.

2
a FSI of 25 can become fully involved and reach flashover in an extremely

short time with a rather modest ignition source [2], even though the

contribution to fire spread of any interior finish material with a FSI

of 25 or less has been considered relatively low.

This anomaly is due in part to the short time to ignition and the

rapid flame spread rate along low density combustible materials. Although

their short time of ignition and rapid flame spread are readily observed

during a tunnel test, these attributes have generally not been reflected

in a high FSI. The new method of calculating the FSI, adopted in 1977,

based on the area under the distance versus time curve, still falls

short of reflecting the potentially severe fire hazard due to rapid

ignition of low density combustible materials.

Several test procedures have been proposed to measure the ignitability of materials. These tests use different types and levels of fire

exposure, different specimen sizes and orientations, and varying criteria

for determining ignition. The exposures may include external radiation,

flame contact, hot air, or some combination of these. The ignition may

be piloted or unpiloted; it may be transient or sustained; it may be

glowing or flaming. The ignitability may be reported in terms of the

temperature of the surface at the time of ignition, the minimum incident

heat flux required to produce ignition, or the time required for a

prescribed evidence of ignition under a standard exposure. The choice

2 Flashover is defined as the time at which thermal radiation levels have

become high enough to ignite light combustibles on the floor. This occurs as approximately 25 kW/m^.

3
of test conditions usually depends on the fire scenario of concern.

There is no universal ignition test that is applicable to all situations, nor should there be. A proposed ISO (International Organization

for Standardization) ignitability test uses a radiant exposure of a

horizontally mounted specimen with an intermittent pilot and reports the

time to ignition at five flux levels [3]. By extrapolating these data

along the best-fit straight line, a "minimum exposure level for ignition"

is determined. ASTM D 1929, an ignition test for plastics, uses a hot

air exposure and records the minimum temperature of the air surrounding

the surface which will cause piloted and unpiloted ignition of the gases

within the enclosing furnace [4], The ease of ignition test described

in this report measures the time-to-ignition of a vertical surface

exposed to a flame with thermal radiation reinforcement from a facing

specimen. Materials which Ignite rapidly and spread flame quickly have

short Ignition times in this apparatus. The time- to-ignition of a

combustible material depends upon the time required to heat its surface

to the pyrolysis temperature. This time is an increasing function of

the thermal inertia, i.e., the square root of the product of the thermal

conductivity, density, and heat capacity.

This ignition test was designed primarily for evaluating interior

finish materials located on walls and ceilings. During the development

of a compartment fire, flame contact from a burning item (wastebasket,

chair, etc.) may occur on these surfaces. The vertical orientation of

the specimens in the test is a direct simulation of the more common wall

exposure situation. It also is expected to provide relative ignition

4
times for ceiling (horizontal facing down) configurations, although the

flame exposure of the walls and ceilings will be somewhat different.

The apparatus does not simulate the fire exposure for flooring materials.

The times between the initiation of the exposure flame and (a) a

flame attachment to the specimen surface and (b) the contribution of

fuel, or volatile pyrolysis products, to the exposure flame are determined. The test is intended to compare the ease of ignition of different

interior finish materials and to supply necessary input data on ignition

to computer models which will be used to predict the fire growth in

rooms with combustible walls or ceilings. This information, combined

with a material's heat release rate, flame spread rate, potential heat,

and thermal properties can be used to provide a more realistic assessment

of its potential contribution to a room fire. However, this test is not

intended to serve as a general flammability or combustibility test but

rather to provide specific information on the ignitibility of a material.

This report provides (1) a discussion of the parametric effects

related to the test procedure, (2) ignition test results which illustrate how the test method discriminates between the ignition sensitivity

of a variety of building materials and (3) validation of the test against

results obtained from full-scale fire tests.

5
2. TEST PARAMETERS

2.1 Specimen Size

The width and height of the specimen, 140 x 152 mm (5.5 x 6 in),

was selected to provide a representative sample of the material that

could easily be used in a bench test. The thickness was chosen to be

that at which the material is normally used because it is expected that

the thickness might influence the time to ignition. Tests were conducted

to evaluate the adequacy of the specimen height. Four materials were

chosen to study the effect of the specimen height on the time to flame

attachment: 4-mm (5 /32-in) prefinished pl3rwood, 6-mm (1/4- in) hardboard,

13-mm (1/2-in) wood fiber ceiling board, and 16-mm (5/8- in) type-X

gypsum board. Because of the limited supply of materials, three tests

were conducted with 140 x 300-mm (5.5 x 12-in) specimens for each of

the materials. Test data for two of the 152-mm (6- in) high specimens,

4-mm (5 /32-in) prefinished plywood and the 6-mm (1/4-in) hardboard, were

taken from the series of tests exhibited in Table 5. The 13-mm (1/2-in)

wood fiber ceiling board and 16-mm (5/8- in) Type X gypsum board specimens do not represent the same materials as those listed in Table 5.

The average flame attachment times for the two specimen sizes, shown in

Table 1, display only slight differences. Statistical t- tests conducted

on each set of specimen data indicate that there is 95 percent confidence that the specimen size had no affect on the time to flame attachment.

The size of the specimens was, therefore, set at 140 x 152 mm (5.5 x

6 in) .

6
2.2 Specimen Conditioning

The purpose of conditioning is to ensure that all specimens are

evaluated under comparable conditions which are appropriate for a

particular study [5], The fire behavior of some materials will vary

markedly with their moisture content which can vary greatly depending

upon the relative humidity. Lee, Loftus, and Gross [6] showed that the

moisture content has a strong effect on the surface flammability of

cellulosic materials.

During the early developmental period of the ease of ignition test

method, a study was conducted by Parker, Brackett, Willard, and Zile on

the effect of humidity on the ignition of some typical room finishing

materials [7]. The first condition tested was 23°C (73°F) at 50 percent

relative humidity for 17 days; the second was one day in a forced hot

air oven at 60°C (140“F), and the third was six days in the 60°C (140°F)

oven. The last condition was sufficient to drive off 6.8 percent by

weight of water and cause a reduction of 50 percent in the time to

ignition of wood fiberboard. Substantial reductions in the ignition

times of other cellulosic materials were also observed.

Data for 20 mm (25/32 in) solid red oak taken with the present

apparatus are shown in table 2. It is important that a standard conditioning procedure is adopted for comparative purposes. It is recommended

that these conditions be predrying at 60°C (140“F) for 24 hours followed

7
by reaching weight equilibrium at 23 + 3°C at a relative humidity of 50

+ 5 percent. The specimens should be conditioned in this environment

until they reach a rate of weight change of less than 0.1 percent per

day.

2.3 Spacing Between Specimens

During the early development of the ease of ignition test apparatus,

the specimens were positioned with a 22-mm (0.88- in) space between them.

The flame between the specimens was relatively laminar. The flame

impinged across the entire surface of both test specimens. While conducting tests on a wide range of materials, it became apparent that the

specimen spacing was too close. It was found that the spacing did not

provide room for the expansion of materials treated with intumescent

finishes. By increasing the distance between the specimens to 50-mm

(2.1-in), the required space for expansion was provided. The increased

distance between the specimens provided a more desirable exposure flame.

It was more luminous and turbulent and no longer impinged constantly on

the specimen's surface. The exposure was more like that of diffusion

flames produced by incipient burning of furnishings and building materials in a typical room fire.

2.4 Ventilation

An overall view of the test chamber is shown in figure 1. The

chamber is designed with two openings, one on each side, near its bottom.

8
as noted in figure 2. These openings allow the air required for combustion of the gas and the specimen to be drawn in by means of convective

currents that develop during the test. This air flow also helps to cool

the test chamber. A detailed description of the chamber is contained in

appendix A. The area of the table between and below the face of the two

specimens is cut away leaving a sharp edged opening so that combustion

air can be drawn up by free convection. Combustion air is also entrained

along the vertical openings between the specimens. An opening in the

top allows the heated air and products of combustion to flow into a

chemical hood where they are removed from the test area. The air requirement for combustion will vary with the type of specimen and its

heat release rate. For typical materials which would be tested in this

apparatus, 98 kJ (93 BTU) of heat are produced when all of the oxygen is

3 3 consumed in 0.028 m (1 ft ) of air. The maximum heat release rates are

2 expected to be approximately 200 kW/m although the specimens would

usually be extinguished before this value is reached. The area of the

2 2 two specimens is 426 cm (66 in ) , so that the total rate of heat production from the specimens would be 8.5 kW (485 BTU/min) . The air

requirement would be 2.5 L/ s (5.2 ft /min) for the specimens. It takes

10 volumes of air to burn one volume of methane. The total gas flow to

3 the igniting flame is 0.2 L/ s (0.42 ft /min); therefore, the air re3 quirement is 2.0 L/ s (4.2 ft /min) for the igniting flame. The total

3 air requirement for combustion would be 4.5 L/s (9.4 ft /min) assuming

that the specimens were allowed to reach their peak burning rate with

the igniting flame on. The air flow rate through the chamber, as

measured with a hot wire anemometer at the inlet air openings, during a

9
3

test is approximately 15.5 L/s (33 ft /min), which is about three times

the air required for combustion. This rate is primarily controlled by

the convective currents created in the test chamber, but it will be

influenced by the amount of draft provided by the chemical hood. Therefore, the air flow through the hood should be maintained at a level that

will adequately remove the products of combustion without affecting the

air flow through the ignition test chamber.

2.5 Cooling Blocks

Water-cooled brass blocks were incorporated into the test apparatus

to (1) maintain the specimen assembly exposed to the flame at a relatively constant temperature during extended periods of use in order to

reduce variations in temperature and radiation that could result in

changing test conditions, and (2) reduce the chances of burn injury to

test operators accidentally contacting the hot test frame.

2.6 Gas Supply

2.6.1 Type of Gas

Initially, the gas used for the exposure flame in the ease of

ignition apparatus was typical city gas (consisting principally of

methane plus small amounts of other components) which is used for home

and industrial heating in the Washington, DC area. City gas varies

considerably in different geographical areas of the country. The

10
3 3 heating value can vary from 22.3 to 37.2 MJ/m (600 to 1000 BTU/ft ).

Since these variations may have a significant influence on the properties

of the exposure flame it was decided to consider the use of bottled CP

methane, for the ease of ignition test. A series of experiments was

conducted to compare the flame and exposure characteristics of CP methane

and the city gas used in Washington, D.C.

The flame temperature and total incident heat flux on the specimen's

surface were measured. CP methane, which is 99.0 percent pure, provides

a gross heating value of 37.7 MJ/m^ (1012 BTU/ft^) at 15.5°C, 101 Pa

(60°F, 29.92 in Hg) . Since the city gas pressure at the ease of ignition test apparatus is 320 mm H

2 O (12.5 in H^O) and the tank pressure of

CP methane is 15.6 MPa (2265 psig) , a regulator system was used to

reduce the CP methane gas pressure to the working pressure of the ignition apparatus. The gross heating value of city gas used in these

3 3 experiments was measured to be 37.5 MJ/m (1009 BTU/ft ).

A 0.127-mm (5-mil) chromel-alumel thermocouple was used for the

determination of the apparent flame temperature. Measurements were

recorded along the central vertical plane of the exposure flame. The

thermocouple was placed midway between the specimens at three locations:

one at the bottom edge, one at the center, and one at the top edge of

the specimens. The average flame temperature for the city gas was 671°C

(1240°F) and for CP methane it was 666°C (1230°F), a reduction of less

than 1 percent. The temperature distribution along this central plane

can be seen in table 3.

11
The total incident heat flux was measured with a copper disk calorimeter located in the right specimen test frame. (See figure 3 and

also description of calorimeter in appendix B.) A series of six tests

was conducted with gas flow rate of 0.20 L/s (25 SCFH) for city gas and

for CP methane. The results shown in table 4 indicate that there was no

difference between city gas and CP methane in this experiment.

Further review of the various grades of methane gas shows that

Technical Grade methane, 98.0 percent pure with a heating value of

3 3

37.7 MJ/m (1012 BTU/ft ), is approximately equivalent to CP methane in

quality but costs substantially less. With the desire to reduce costs

while providing the consistent gas quality required for making comparative measurements of specimens within a laboratory and between different

laboratories. Technical Grade methane was used as the primary fuel for

the ease of ignition test.

2.6.2 Incident Heat Flux versus Gas Flow Rate

Tests were conducted to evaluate the effects of gas flow rate on

the total incident heat flux to a specimen surface. The heat flux was

measured at six different gas flow rates ranging from 0.1 to 0.3 L/s (13

2 to 39 CFH) . As seen in figure 4, the heat flux was 47 kW/m at the

highest gas flow rate.

12
2.6.3 Flame Attachment Time versus Total Heat Flux

This test method was designed to evaluate the ignition sensitivity

of building materials in contact with flames from incidental or low

energy fires. A typical example is a wastebasket or funiture fire

adjacent to a wall. In the case of fires in the corners of a room or in

narrow spaces between walls and furniture, there can be an appreciable

exchange of heat between the exposed surfaces. A study by Gross and

Fang at NBS [8] with wastebasket fires showed that the maximum Incident

2 heat flux at the edge of the flame could be as high as 53 kW/m

2 (4.6 BTU/ft sec) depending on the size and type of wastebasket, fuel load,

and fuel burning rate. On the basis of these experiments, the average

2 2

heat flux of 32 kW/m (2.8 BTU/ft sec) was selected. This was obtained

with a combined gas flow rate from both burners of approximately 0.2 L/s

(25 CFH) with CP methane. The heat flux into the specimens was not

distributed evenly across the surface. Heat flux measurements, with

2 specimen spacing at 50 mm (2.1 in) and an average heat flux of 32 kW/m

2

(2.8 BTU/ft sec), showed a variation of 24 percent over the 75 mm (3 in)

span between the lower and upper copper disks of the calorimeter used

for calibrating the apparatus. (See appendix B for a detailed descrip2 tion of the copper disk calorimeter.) The higher heat flux, 36 kW/m

2

(3.1 BTU/ft sec), was obtained from the lower copper disk; and the

2 2 lower heat flux, 29 kW/m (2.5 BTU/ft sec), was obtained from the top

disk.

13
Tests were conducted to evaluate the effects of changes in total

incident heat flux on the flame attachment times on 13 mm (1/2 in) wood

fiber ceiling board as seen in Figure 5. The incident heat flux was

measured with the copper disk calorimeter. Tests were performed with

gas flow rates of 0.140, 0.220, and 0.275 L/ s (18, 28, and 35 CFH)

.

3. IGNITION CRITERIA

3.1 Flame Attachment

The ignition sequence begins with the flame exposure of the specimen. As the surface temperature approaches 100°C (212 °F) free moisture

near the surface is evaporated. As the surface dries and continues to

rise in temperature, surface degradation begins. Degradation is most

often recognized as the discoloration of the surface associated with

charring. With some materials, bubbling of the surface, swelling,

shrinkage, and/or cracking may be experienced before charring occurs.

These conditions, as well as any unusual observations, are reported with

the test data. Smoke generally is produced when surface degradation

begins. As the specimen continues to heat, volatiles are emitted at an

increasing rate until they are either ignited or the specimen is completely depleted. When the mass flow rate of volatiles per unit area

reaches some threshold value, they are ignited by the exposure flame.

With some materials a thin, transient, transparent flame is seen above

the specimen’s surface just before flame attachment is observed. However, the test operator, by direct observation of the specimen's surface.

14
records the flame attachment time only when a flame becomes fixed to a

point on the specimen’s surface. The attached flame is generally characterized as being opaque and slightly brighter than the gas exposure

flame. In some cases, rather than spreading across the surface, the

flame will only attach at small, isolated areas and, thus, provide very

little fuel to the exposure flame. On the other hand, high velocity

streams of volatiles issuing from cracks developed in the specimen

surface will sometimes provide a significant amount of fuel to the flame

before a flame attachment is observed.

3.2 Fuel Contribution

The problem of describing ignition using a single definition related only to flame attachment became apparent while conducting tests on

low density foam insulation materials. As can be seen in table 5, these

materials provide a significant fuel contribution before flame attachment is achieved. This results from the fact that large quantities of

high velocity combustible vapors are released from the specimen, and

burning takes place away from the specimen's surface. A series of

experiments was conducted with thermocouples and phototubes to determine

the best method for recording the initiation of this fuel contribution.

A single thermocouple located at different points between the specimens

and a thermocouple grid located in the exposure flame above them were

used to measure the temperature rise when the specimens begin to release

fuel. Phototubes were also positioned at different locations inside the

test chamber. The results of these experiments showed that thermocouples

15
had excessive noise due to flame fluctuations. The phototubes also

produced noise, but at a much lower level due to the averaging effect of

viewing a large flame area. By placing additional capacitance into the

phototube circuit, the high frequency noise was reduced to an acceptable

level. Also, to insure that the phototube output was showing a definite

increase in luminosity of the flame above that which might be caused by

longer period fluctuations, the time of fuel contribution w,as picked

from a point on the phototube output curve 25 percent above the base

line obtained with noncombustible ceramic specimens. A phototube record

showing the determination of the time to fuel contribution is presented

in figure 11. The type 922 phototube was selected because it has an S-1

surface, which has a good response to near-infrared radiation emitted by

the combustion products. (Since this work was completed, experiments

with a row of thermocouples just above the top edge of the specimen and

a small distance out from the surface may give even more reproducible

results than the phototube.)

The time to fuel contribution is basically controlled by the amount

of combustible volatiles available and the thermal properties of the

material. With wood and other cellulosic building materials, flame

attachment usually occurs before the time when a significant quantity of

fuel is contributed to the exposure flame. Therefore, the time to fuel

contribution can occur before or after flame attachment. However, it

may not occur at all with materials which release small quantities of

combustible volatiles.

16
4. IGNITION DATA ON MATERIALS

Ignition tests were conducted on a variety of materials, some of

which were painted and others which were treated with flame retardant

chemicals. The results can be seen in table 5. The variation in fuel

contribution times with several materials is illustrated on a linear

time line in figure 6. In general, the fuel contribution time for a

cellulosic product is seen to increase with density. The time to ignition depends on (1) the thermophysical properties, particularly the

product of the thermal conductivity, density, and specific heat, (2) the

thermochemical properties, and (3) the surface properties, particularly

the absorptivity, which determine the radiation heat transfer and the

surface roughness which affects the convective heating and the effective

area. Coatings alter the surface properties and, in some cases, provide

a thin layer of much higher or lower heat of combustion than the substrate material. The coating may also contain flame inhibitors which

are released into the gas phase. In the case of intumescent coatings,

the thermophysical properties of the expanded coating are also Important

in limiting heat transfer to the substrate. The effect of surface

coatings on lauan plywood can be seen in table 5 where selected intumescent coatings increased the ignition times by a factor of five.

5. COMPARISON WITH FULL-SCALE TESTS

Perhaps the best single index of the fire hazard of a room would be

the time required to reach flashover once a significant fire developed.

17
Rapid fire buildup can occur as a result of the contribution of combustible interior finish materials. A possible scenario, in this case,

would be the ignition of a newspaper on an upholstered chair. After an

initiation period the fire might build up to the point of flame impingement on the wall. After some ignition delay time that could be determined

by the ease of ignition test, the wall would start contributing fuel,

and flames would spread at a rate depending on the thermal properties of

the wall material and its heat release rate. Since the time to ignition

also depends on the thermal inertia (square root of the product of the

thermal conductivity, density, and specific heat) data from the ease of

ignition test, and the heat release rate test should provide some indication of the time required for a room lined with this material to

reach flashover.

In order to demonstrate the usefulness of the ease of ignition test

as one of the indicators of the performance of an interior finish material in a room fire, the time to flame attachment recorded in the test is

compared in table 6 and figure 7 with the time of wall ignition in

several full-scale room fire tests series carried out at NBS and at

Underwriters Laboratories (UL) . These tests include the corner room

test series conducted by Fang [9], the mobile home tests conducted by

Budnick [10,11], and the full-scale room fire tests conducted at UL [2].

The included tests were limited to those using wood cribs as an ignition

source; tests in which upholstered chairs were the ignition source had

too much scatter and were not included. Even with this limitation,

considerable variations are experienced in the full-scale fire tests.

18
Part of the spread in the data is due to fire growth variations in the

wood cribs and part is due to the difficulty of accurately determining

the exact time of wall involvement in the full-scale tests. One other

variation that influences the results presented in table 6 and figure 7

is that the ease of ignition test submits specimens to a relatively

constant exposure, while in a typical fire environment incident heat

flux is constantly changing.

It should also be noted that results would probably be somewhat

different if the materials were tested using a heat flux other than

32 kW/m (2.8 BTU/ft sec). However, it is important to remember that

the heat flux exposure chosen for this test is based on research by

Gross and Fang [8] on low intensity fires which are often associated

with Initial fire growth in rooms. Figure 7 shows the data compared to

a 45 degree line which has been adjusted to allow for a 30-second delay

in crib fire buildup. Taking the average wall ignition delay times for

a given material and allowing for the inherent delay time required for

the fire to buildup in the wood crib, figure 7 shows that the ease of

ignition test can provide a reasonable estimate of the ignition delay

time of the wall lining material exposed to a wood crib or similar

furnishing fire.

Table 7 shows a comparison of the fuel contribution times in the

ease of ignition test with the times of wall involvement and flameover

in the full-scale room fire tests with the 9.1-kg (20- lb) cribs at UL

[2], The peak heat release rates measured in the NBS heat release

19
2

calorimeter at an incident flux of 30 kW/m are also included. The

times, listed in this table, at which flame movement beyond 1.4 m (4.5

ft) was first reported in the tunnel provide an approximate measure of

the time to fuel contribution for another incident flux and specimen

orientation.

Although a limited number of tests were run, the range of materials

and results illustrates the usefulness of the ease of Ignition test.

Flames extended beyond the doorway much earlier with the foam plastic

materials A and S than with the plywood material H, as would be expected

from the ease of ignition test results even though the flame spread

classification (FSC) and the heat release rate were much lower for the

plastics than for the plywood. The time differences are more dramatic

if the fire buildup time in the crib is taken into account. However,

the ease of ignition test results alone suggest that G and H would

flashover about the same time. While the ease of ignition test provides

an indication of the thermal inertia of the material which is one determining factor in the flame spread, the other factor is the heat release

rate which is very low for material G.

Material R has a low thermal inertia but its fuel production rate

through the foil face is insufficient to establish a flaming ignition.

Its heat release rate is also very low so that full flame involvement was

not observed in the room test. The exposure was large enough in the

region of the burner of the tunnel to burn through the foil and Induce a

flaming ignition at 20 seconds. Although this also occurred in the region

20
of the wood crib in the room test, the exposure outside this region was

insufficient to destroy the integrity of the foil and propagate the

flame. It is important to consider the heat release rate as well as the

time to fuel contribution.

6. PRECISION AND ACCURACY

As with other tests, operator skills and good laboratory techniques

are required for obtaining the most accurate results and maintaining

good repeatability in relation to the observation and recording of flame

attachment time and for properly determining the time to fuel contribution

from the chart record.

It is known that natural and manufactured products are not always

uniform. Materials generally contain many imperfections, such as inconsistency in density and quantitative and qualitative changes in chemical

composition. For example, wood changes density near knots and with

annual growth. Chemical changes are also associated with these physical

variations. Manufactured products also reflect irregularities even

under closely controlled process conditions. Some of these may result

from variations in raw materials properties, feed problems, equipment,

and human failures. The result of the above variations may influence

the ignition sensitivity of the material.

21
To demonstrate the precision of the test procedure with a relatively uniform material, twelve tests were conducted on the standard

hardboard used for calibrating the ASTM E 162 "Test for Surface Flammability of Materials Using a Radiant Heat Energy Source" (see table 8)

.

The results show relatively good repeatability. The mean average for

the time of flame attachment was 109 seconds and time of fuel contribution was 138 seconds. The time of flame attachment exhibits a repeatability coefficient of variation of 4.0 percent while the time of fuel

contribution has a repeatability coefficient of variation 3.7 percent.

With materials that are not as uniform as the standard hardboard it can

be expected that the variations will be larger. Coefficients of variations for two materials listed in table 5 demonstrate the increased

variation. A 4-mm (5/32-in) prefinished lauan plywood specimen has

coefficients of variation for flame attachment time of 8.1 percent and

fuel contribution time of 8.2 percent. Another lauan plywood with a

fire retardant vinyl surface exhibits a repeatability coefficient of

variation for flame attachment time of 12 percent and for fuel contribution time of 8.6 percent.

7 . SUMMARY

An ease of ignition test using a flame exposure has been developed

which can be used to evaluate the ignition sensitivity of a wide range

of interior finish materials. The specimen configuration and gas flame

simulates the type of diffusion flame exposure which is experienced by a

wall surface when an item of furniture is burning in the corner of a

22
2 room. The incident heat flux imposed in the test exposure is 32 kW/m

based on the experiments of Gross and Fang [8], but it can be varied

2

from 20 to 45 kW/m by changing the burner gas flow rate. A minimum of

four tests are conducted to obtain an average time to fuel contribution

and time of flame attachment to the surface. The time to fuel contribution is defined as the time when the recorded output of the phototube

viewing the exposure flame is increased by 25 percent above the base

line (another method of determining the time to fuel contribution using

thermocouples is being investigated) . The time to flame attachment is

determined by direct observation of the surface.

This test method allows for a good view of the specimen's surface

during the test. Observations during tests are recorded because they can

provide additional insight as to the ignitability of a material during a

room fire.

The comparison of the time to flame attachment and the reported

times of ignition of the wall materials in 22 full-scale room fire tests

with a wide variety of interior finish materials and test configurations

indicates a reasonable agreement between the ease of ignition test with

the exposure given above and full-scale room fire tests although there

is a large amount of scatter. The difficulty in estimating the involvement times of the wall as well as variations in the buildup of the

ignition sources in the room were probably responsible for a large part

of the observed data spread.

23
As can be seen in table 5, there are large ranges in the flame

attachment and fuel contribution times of typical interior finish materials.

Since the ignition of interior finish materials often results from

exposures to similar fire environments, the times to ignition measured

in this test may be used to predict their time of involvement in a room

fire and to rank them accordingly.

This test is not intended to serve as a general flammability or

combustibility test but is designed to provide information on the ignitability of a material which, when combined with its heat release rate,

flame spread rate, potential heat, and thermal properties, can be used

to provide a more realistic assessment of its potential hazard in a room

fire

.

In particular, one should not expect a correlation between the time

to ignition by this test and the flame spread classification which

depends on other attributes of the material. Materials which have short

ignition times and rapid flame spread rates due to their low thermal

inertia do not necessarily have high flame spread classifications in the

E 84 tunnel test nor do they necessarily have high heat release rates.

8 . ACKNOWLEDGMENT

We are indebted to Mr. Roland Willard who fabricated most of the

test apparatus.

24
9 . REFERENCES

[1] Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM E 84-81a, American Society of Testing and

Materials, Philadelphia, Pennsylvania (1981).

[2] Flammability Studies of Cellular Plastics and Other Building

Materials Used for Interior Finishes, Underwriters Laboratories,

Inc., Northbrook, Illinois (June 1975).

[3] Fire Tests on Building Materials and Structures, International

Organization for Standardization, Document No. ISO/TC92/531.

[4] American Society for Testing and Materials, ASTM D 1929-77, ASTM

Book of Stds. Part 35, pp. 649-654 (1978).

[5] Masters, T. W., and Tryon, W. , A Methodology for Establishing

Conditioning Requirements for Building Materials and Composites,

Nat. Bur. Std. (U.S.), NBSIR 75-767 (October 1975).

[6] Lee, T. G., Loftus, J. J., and Gross, D. , Effects of Moisture on Surface Flammability of Coated and Uncoated Cellulosic Materials,

American Society for Testing and Materials, STP No. 385, pp. 112-123

(1965)

.

[7] Parker, W. J., Brackett, D. E., Willard, R. E. and Zile, R. H., A

Preliminary Investigation of the Effects of Humidity on the Ignition,

Heat Release, and Smoke Density Tests for Typical Room Finish

Materials, Nat. Bur. Std. (U.S.), NBSIR 73-139 (March 1973).

[8] Gross, D. , and Fang, J. B., The Definition of a Low Intensity Fire,

Nat. Bur. Std. (U.S.), NBS Special Publication 361, pp. 677-686

(1972).

[9] Fang, J. B., Fire Buildup in a Room and the Role of Interior Finish

Materials, NBS Technical Note 879 (June 1975).

[10] Budnick, E. K., Fire Spread Along A Mobile Home Corridor, Nat. Bur.

Std. (U.S.), NBSIR 76-1021 (July 1976).

[11] Budnick, E. K. , Mobile Home Living Room Fire Studies: The Role of

Interior Finish, Nat. Bur. Std. (U.S.), NBSIR 78-1530 (Sept. 1978).

25

<aA

M

3

0-1 ca

ccDo< <

c

o

c

CO

14-1 o

3:CJ

4-1 (U

c/a

27

FRONT

VIEW

OF

APPARATUS
FRONT VIEW

NOTE: Not to scale

Figure 3. Copper Disk Calorimeter

28
0 16

AVERAGE HEAT INPUT RATE (kW|

4 8 12

Figure A

.

Total Incident Heat Flux versus Gas Flow Rate

29
INCIDENT HEAT FLUX |kW/m^j

Figure 5. Incident Heat Flux vs. Time to Flame Attachment

for Wood Fiber Ceiling Board

30
FR

POLYURETHANE

FOAM

|2.5

PCFj

r

PVC

NITRILE

RUBBER

FOAM

|7.2

PCF|

CML

31

Figure

6.

Fuel

Contribution

Times

fora

Variety

of

Materials
Figure 7. Flame Attachment Times in Full Scale Tests Versus Flame

Attachment 'T'imes in the Fase of Ignition Test

• Ref. (7,8) iRef. |6j A Ref. (2)

32
33
34
EXPOSURE

922

PHOTOTUBE

35

Figure

10.

Phototube

and

Time

Marker

Circuits
36

Figure

11.

Phototube

Record

for

32

Kg/m3

(2

PCF)

Polyisocyanurate

Foam
Figure 12.

Schematic Diagram of the Operation of the Copper Disk Calorimeter.

37
3/4

38

Figure

13.

Drawing

of

the

Copper

Disk

Calorimeter
39

Figure

14.

Chart

Record

of

the

Incident

Flux

Measurement
TABLE

1.

EFFECT

OF

SPECIMEN

HEIGHT

0)

4-1 d

o

d uO 0) 0) rH ro oc o d • • •

)-i o CO

0) dM-l

14-4 O

+ 1 +

+j C D

•H S

d rC ^

CM CU O W

rH S CC ^ w .H 4-1 CJ 4-J Q) s <D <d 6 BO- *H

I W QJ H

o e O

m

cd

vOmd m vo

CJ^ m \£)

\£)

4Js cl- dj a CO

0 4-10) g

<U C 6

a Ou "H

I CO 0) H

M B

n cO

CMm<f iH m

(Ti lO| vD

•d

0) -dm

•Hd

4-tQJU

P4

I—

1

d T3 d •H O

•H I 2

d <N >

<u ro >->

4-1 rH d m P-i S

d

nd d

d Xi d •H o fi-i X

X3 X 1 XI X d 0) X

d o d a d

d o o X d

fd :s P3 H O

PQ

V ^ bO d d d d B

•H •H H X d

1 1 f-H 1 w

tH 00 ocu

I—1 iH O m o

^—

s-*" '—^

I ro

40
TABLE 2. EFFECT OF CONDITIONING ON IGNITION OF RED OAK

Condit ioning

Method

Fuel Contribution Time (s)

17 days

23°C (73“F) 50% RH 166

1 day in Oven

60°C (140°F) 131

6 days in Oven

60°C (140°F) 106

41
TABLE 3. COMPARISON OF TEMPERATURES PRODUCED BY CITY GAS AND METHANE

IN THE CENTRAL VERTICAL PLANE OF THE EXPOSURE FLAJIE

Thermocouple Height

in Relation to the City Gas CP Methane

Specimen (°C) (°C)

Top 638 621

Mid-Height 693 716

Bottom 682 660

Average 671 666

42
TABLE 4. COMPARISON OF INCIDENT HEAT FLUXES FOR CITY GAS AND METHANE

CITY GAS CP METHANE

INCIDENT HEAT INCIDENT HEAT

FLUX FLUX

(kW/m^) (kW/m^)

34 32

30 31

32 32

33 32

33 30

30 35

AVERAGE 32 AVERAGE 32

43
TABLE

5.

TIMES

TO

FLAME

ATTACHMENT

AND

FUEL

CONTRIBUTION

CO iJc

CDO

CJ cou

CO •H>Q

T3U

CO XJc

CO

4-) W

I—I c

cu o 3

[3L| 4-1 3 O Xi

4J ‘H

)-< (D 4-J e c

*T-|

O

H

O

O o m

CNo

,-H 0) •H . O (U n3 CL <u x: bO

<D CO CO CO CO C <D U 4-1 3 x: Xi GC 01 3 C •HOG •H M o x: c a C CO

(1) nj g

•H V4 O O

0) 3 a «H

pL 4-1

O CO s

rH c

(U o 3 *H

L-i 4-1 3 O XI 3 -HM

4J

W 3

•r>

O 5 O

O o M

CM

0)GO3

L4(1) ><

Q)3

pHO

4J

0)eH 3O

•H

4-1 3

•H>3C

T)

V43

Td33

4-1 CO 3a3

i-H Pho

4-1 3aHH 3

GO3U3>< 3a3

t—j

pLo

4J3aH

4-4o

Pi3

Xia32 33a

x:

CJ3 CM

c^

CM

vO

CM

Om o

o> o

vO 3 Td 3 3 I ^

•H CO O 3 3 H a

CO33 CO Q a

O

CO

O

Pi

4-1 4J 3 4J 3 3 3 rH 3 3 3 3 •H 3

'3 Pi 33 rH Td

u 0 4J 3 3

Pi 3 Pi rH Pi 3 Ph 3 rH rH 3 3 3 3 rH Pi CP *H *H

4J 3 3 4J

O 3 U 3 3 a 3 < Pi Pi 3 rH o 3 O 3 rH 0 3 3 PI 4-1 Oi •H cd 3 *H Cei rH •H 3 3 a •H •H 3 4J 4J 4-1 3 4J H \ 2 2 3 3 O 3 3 3 3 3 CJ 3 £ U 4J •H Pi 1^ Pi Pi rH Pi rH 3 O 3 iJ CJ CJ U •H 3 3 •H 3 3 *rH 3 3 rH CO 3 > > 3 P-( 3 W pP 3 to Pl 3 CO < *H rH CP a pui 4J 3 3 3 3 3 3 CP 3 3 3 jd M M x: M rH 0 ^ O 2 3 4J z 3 O 3 4J z 3 o Pi *H 3 Pl 3

•H 3 U

a •H

OO < *H 3 O CO •H CP 3 4J •H •H

Pi

H z W *H z Pi •H z rH 3 Pi CM 3 4-1 CM •H 4-1 CM 3 4J rH 33 3 rH rH 3 rH

>v CO 1 >>W 1 >- (0 1 'w«' 3 rH 3 w XI

rH 3 rH 3 rH 3 O rH 3 X5 O f—1

ij s 0 ^ g

O fH ij

g 3 3 3 a 3 g § CU 3D a PL4 CP 33 a CP CP D s P4 O M a E O o o lA m m m m m CM CM CM

44

*0nly

three

tests

conducted

because

supply

of

materials

was

limited.
Average

Standard

Deviation

Average

Standard

Deviation

Time

to

Flame

Time

to

Flame

Time

to

Fuel

Time

to

Fuel

Attachment

Attachment

Contribution

Contribution

o

CJ

<v o a •H

CL 4J O d •H U fH 0 c rH W (U •rl to CO D 4J • *ri

4-i U~l s 'O c

CO (V * * to o

0) 0) H c

4J i-i •H 'O CO O U d u

(V tM C CJ o u CO d a; 0 u rH o (V o u o o c u

00

fO oCN

-vT

COo

m

cncn

00

00

00

vo

<r

CNto o o ON

+-

CO u CJ o

00 ClH CN 2; 2

p*^ ro

lO C7N m m

o CM m o CO

CM 00 CO

CN

00 iH

<r m

CN00

CO

CO

CN CN

CO

to

«

C X)

(V <v O 0)

QJ H

a

CO

c

(U ro Q 6

O

O

5

(U

»H <U CN W

— ‘H •H C

lO

CO uo m vO r—

i

00 vO

•ON vO <r to CM CN 00 CO

MT to sD r-. r-- CM CO

X3 'd 'd -d d d

0 o o a) o o

t3 0 o o <D u o o

(U s s U cd s u d M

•H d d) dj d) CO r—

1

TJ 1^ •iH rH JO U JO

•rH pL. (U P-. p-l B CU CU •H d •H d V Cd •H pL. 0) ‘H d Cd d d d d 4H d U Cd u d U-l cd d) cd Cd •rH cd d cd d d Pm d •H d)

<V d M d d iH d •H d CN •H 0 o Cxh u

cd 4J cd O cd Cd 1 Cd o o Cd

pL. no hJ d h3 CN d rJ d (X h3 d p^ 3 d 3 (U O d) O •tH d d u 0) M

/-N O /»—

s

'd y—

N

• > s cd 4J S cd Cd y—

S

rH H

d S d /-~N Cl) d o Cl) d u d d M d d o d •H

•H •H d tH 'w' •M o •rH PQ 0) iH CQ (D •rH m •H H

•H CO z d cd o o c

CN vO •H PC CN 6 cd tM CN CO CO CN CO CO CM oo CM OO Cd CO i-H <r d CO B •d u CO u (U CO 4J 0) d d d

d — iH ''

u d cd g cd g «-H •H rH •H u

lO cO CO U-< 1 LO i-H Cd CO to o d to o d 'w' rH 'w' iH Cd d 0) 'w' to u CJ CJ 4J •H *H 4J

(0 u hJ 0) 0 d d g 0) g 0) (1) h3 g B Cu :o g o cd u B CN M B CM M g CJ g CJ Pd B B B

CO CO m \o •<f rH iH

45

*0nly

three

tests

conducted

because

supply

of

materials

was

limited.

tNFA

=

No

Flame

Attachment;

NFC

=

No

Fuel

Contribution.
Average

Standard

Deviation

Average

Standard

Deviation

Number

of

Time

to

Flame

Time

to

Flame

Time

to

Fuel

Time

to

Fuel

Density

Specimens

Attachment

Attachment

Contribution

Contribution

•HU

c

o

COm

o

o*<3-

s£)

B On r**. CO r»* r—

CN CO CO CO CO

a^ rH m vD

tou c c Td •3 Td

1 0 •H 0 D ID D

M u •H X X xi

CO 0 Cd C30 U CO CO to u 4-» *H CO O CO *H •rH •H

0) (V j-i Td o U M d d d

o CO no CO T5 Di OJ o CO • O CO *r4 X -rg X

pa o (U O 0) •U» o 1—

1

x: o O iH M-i 1 U-l 1 Td <D 3 u N-*' (D 3 d 0) c D d

1—

1

'O 0) d 73 d M w ^ PO »H O 00 D a 3d a 35

vj 'Id <U CO 0) CO CD 5

c (D >> >>

•H fO Pi CO Pi CO ^ Pu, Pi g D Pi H - H r U aa CO Td Td U Td *3 Td

(D CD U u Csi CO u M

4-1 ^ d) d Td d Td C 4J -H d CO • >4-1 d CO d CO d CO

CC d d •H (U •H 0) CO fe •H o o U *H o •H 0 •rl O 2 •H O 0) r PQ 3 pa pa OQ

Nd* CO to eg M CO CJ? <N Td CO eg 00 CN

x: •H H CO s B ID 8 ^ E S

jj d CO d fH tH 3 •H f—

1

•H 3 in 3 iH 3

.H o 'w' •H *J 60 1 Vw*” CO w CO w CO to w 0 U-i d 3 a a d a a a

e s d 8 d s rt 0 iJ g ?o a •H i >> i >» g

1 ^ B 6 da i o a D s o < > 8 O S o B o m ro CO CO CO va CO

•—

1

r-i 1—

1

1^ rH rH rH

46

*Only

three

tests

conducted

because

supply

of

materials

was

limited.

tNFA

=

No

Flame

Attachment;

NFC

=

No

Fuel

Contribution.
Average

Standard

Deviation

Average

Standard

Deviation

Number

of

Time

to

Flame

Time

to

Flame

Time

to

Fuel

Time

to

Fuel

Density

Specimens

Attachment

Attachment

Contribution

Contribution

o

T3 OJ

o; ^

9 B o B

pC AJ 0 rH

(A .C O M-i 00 U

C *H M-t 0)

0) iH U

a CA (1) 3

•H 00 CA U >s fO O

0) rH 0 Cu a c 03 X W o T3 0)

(U

o o o o o

Uu f3-> tiH z z z z z

•f-<

z

3

E o Oh Oh m r*. o CO CO \0 hO hO m II w 00 r*^ 00 hO

.X O

Px. z

1 *d Li • «K CA 3-1 d) LI tA 03 CL C

d) a CA O a 03 a d u 3 0) PQ 3 CL 3 a

o CA OS CA CA pH o a U a a CL 0) CL u

'U >> T3 d) 3 3 >> O Jo cd 0 (U o 0) d pX CA (A O Cd O u u

. D ^ pC 4J O CL CL c Z L>

cfl (A (A pc CA 03 cd >> >> O pc *H CA < •H a ‘H Z CQ O O Z T3 X 03 *H u ?s C C d CL C d

a; o -H a <p—

s

s /—s 4J y—

S

•r^ a

jj 4-1 C 4-1 c 3 c c c c c -d ft. cd 03 ^ C •H C •H CA •H OO •H *d •H *H •H c iH Z C |Z> 33 CL c 3-« Li 03 'd Cl

•H vD CM CM *H CM (d O CL sD W CU

f-H *' O pC \ o iH *H M O

rH 'd 'd i-H iH JJ .H pQ -d no 3 Z ^ u N.-P' u 03 a uo 3-1 m H

03 03 C CU 3-1 w 03 cd X II S o o 0 03 a pc: a o O o d

B CQ e cQ B U a to a [h a a (33 H <

a 0 a Cl m CO CO CO Z

CM 00 rH iH 00 00 -H

47
TABLE 6. FLAME ATTACHMENT TIMES IN THE EASE OF IGNITION

TEST AND FULL-SCALE ROOM FIRE TESTS

Flame Attachment Flame Attachment

Time (s) Time (s)

Ease of Ignition Test Full-Scale Fire Test

Reference

Identification*

1 8-mm (5/16-in) 101

Gypsum Board

Printed Surface

2 4-mm (5/32-in) 234

Prefinished Lauan

Plywood with Two

Coats Intumescent

Paint

3 4-mm (5/32-in) 52

Prefinished Lauan

Plywood

4 4-mm (5/32-in) 62

Prefinished Lauan

Plywood

5 6-mm (1/4-in) 124

Prefinished Lauan

Plywood Factory

Intumescent Treated

Surface

6 4-mm (5/32-in) 244

Prefinished Lauan

Pljrwood with Two

Coats Intumescent

Paint

7 4-mm (5/32-in) 82

Lauan Plywood with

0.51-mm (0.020-in)

Fire Retardant Vinyl

Surface

8 4-mm (5/32-in) 87

Lauan Plywood with

0.51-mm (0.020-in)

Fire Retardant Vinyl

Surface

9 8-mm (5/ 16- in) 101

Gypsum Board

Painted Surface

10 6-mm (1/4-in) 59

Prefinished Lauan

Plywood

76

90

100

190

200

60

95

69

75

125

170

290

154

145

60

60

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

[ 10 , 11 ]

*Test program reference numbers found in section 9.

48
TABLE 6 (cont.)

11

12

13

lA

15

16

17

18

19

20

21

22

NOTE:

Flame Attachment Flame Attachment

Time (s) Time (s) Reference

Ease of Ignition Test Full-Scale Fire Test Identification

16-mm (5/8-in) 153 192 [9]

Particle Board 156

Unfinished 186

6-mm (1/A-in) 105 132 [9]

Prefinished Douglas

Fir Plywood

168

4-mm (ll/6A-in) 95 150 [9]

Lauan Plywood

Sanded Finish

198

3-mm (1/8-in) 151 192 [9]

Melamine Finished 210

Hardboard 192

13-mm (1/2-in) 74 126 [9]

Fiberboard Acoustic

Tile Painted Surface

138

50-mm (2-in) Flame

Retardant Polyurethane

Cellular Plastic

1.9 PCF Density

2.6 30 [2]

13-mm (1/2-in) Exterior 126 132 [2]

Douglas Fir Plywood

(Flame Retardant)

105

6-mm (1/4-in) 51 105 [2]

Prefinished Plywood 65

50-mm (2-in) Flame

Retardant Polyurethane

Cellular Plastic

2.5 PCF Density

1.0 14 [2]

50-mm (2-in) Flame

Retardant Polyurethane

Cellular Plastic

2.0 PCF Density

1.0 40 [2]

50-mm (2-in) Flame

Retardant Polyisocyanurate Cellular

Plastic 2.3 PCF Density

1.0 20 [2]

13-mm (1/2-in) Flame

Retardant Wood

Particle Board

225 265 [2]

The ignition delay times for the full-scale fire tests are typically longer than

that experienced with the ease of ignition test as a result of the inherent delay

time required for the fire to build up in the wood cribs.

A9
TABLE

7.

COMPARISON

OF

EASE

OF

IGNITION

RESULTS

WITH

FULL-SCALE

ROOM

FIRE

TESTS

AT

UL

[2]

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50

*These

times

include

the

fire

buildup

time

in

the

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crib.

**90

percent

of

room

area

affected

by

fire.
Test

No.

1

2

3

A

5

6

7

8

9

10

11

12

TABLE 8. PRECISION TESTS WITH STANDARD HARDBOARD SPECIMENS

Time to Time to

Density Flame Attachment Fuel Contribution

kg/m^ Ib/ft^ (s) (s)

1009 63 112 136

993 62 106 134

1009 63 105 132

1041 65 111 141

1041 65 102 131

1041 65 116 145

1025 64 114 140

1041 65 112 140

1025 64 105 135

1041 65 111 144

1041 65 111 143

1009 63 105 131

Average 109 138

Standard 4.4

Deviation

5.1

Coefficient 4.0

of Variation

3.7

51
APPENDIX A

IGNITION TEST APPARATUS

A. 1 Burner and Specimen Holder

A sketch of the test apparatus appears in figure 1 and detailed

drawings in figures 8 and 9. Two specimens 140 mm (5.5 in) wide and

152 mm (6 in) high face each other 53 mm (2.1 in) apart. The burner

consists of two water-cooled brass blocks 114 mm (4.5 in) high, 152 mm

(6 in) wide, and 25.4 mm (1 in) thick, facing each other with a gap of

50 mm (2 in) between them. Methane gas passes into the gap through a

horizontal row of 1.9-mm (1/16-in) diameter holes, 12.7 mm (0.5 in) apart,

located 9.5 mm (0.38 in) up from the bottom of each block and extending

across its width. The holes are drilled into a cylindrical plenum, 9.5 mm

(3/8 in) in diameter, running along the width of the block.

The gas enters the burner plenum through the back of the brass block

with the connection centered on the plenum. One end of 3.2-mm (1/8-in)

i.d. soft copper tubing is fitted to the block, and the other end is connected to a solenoid valve with a 7 . 1-mm (9/32-in) orifice. The brass

blocks also contain a network of intersecting 9 . 5-mm (3/8-in) diameter

holes which provide a path for cooling water. The water leaving the first

block passes through the second one before being discharged into the drain.

A chromel-alumel thermocouple is formed at top of the rear surface of the

second water-cooled block in order to monitor its temperature. The 10 mil

wires are peened into the block at a distance of 6.4 mm (1/4 in) apart in

order to insure that the thermocouple junction is in the block itself.

52
The specimen test frames extending above the two water-cooled blocks hold

the specimens 53 + 1 mm (2.1+0.04 in) apart and shield their edges from

the exposure flame. Each specimen is held against the frame by two 9.5-mm

(0.38-in) wide clamps which contact its back surface adjacent to the vertical edges. The back surfaces of the specimen are open to the atmosphere

except where they are contacted by the clamps. This assembly is attached

to a bottom plate which is mounted on a 406-mm (16-in) long and 254-mm

(10-in) wide table. The area of the table between the two blocks is cut

away so that the air for combustion can be drawn in from below by free

convection.

A. 2 Cabinet

The table is located in an aluminum cabinet 610 mm (24 in) long,

762 mm (30 in) high, and 305 mm (12 in) deep with a pyrex viewing window

in the door. Openings 230 mm (9 in) wide and 76 mm (3 in) high, 76 mm

(3 in) from the bottom of each end of the cabinet admit fresh air.

There is also an opening 108 mm (4.25 in) wide and 140 ram (5.5 in) deep

at the top of the cabinet to permit the escape of combustion products.

The cabinet must be located under an exhaust hood.

A. 3 Spark Igniter

Electrical spark Igniter electrodes are mounted to the table bottom,

and they extend horizontally to the center of the apparatus and then are

bent vertically upward through the opening between the burners. Screw

53
clamps are attached to the top of the electrodes where steel tips are

secured. The electrodes are positioned horizontally and on the same

plane as the gas burner holes. The spark gap is set at 3 mm (0.125 in).

The electric current for the spark igniter system is supplied by a solid

state high voltage induction coil with a built-in DC power supply,

catalog number 79803, which is sold by Central Scientific Company.^

A. 4 Phototube and Marker Circuits

An RCA type 922 vacuum phototube which is used for determining the

time of fuel contribution by the specimen is mounted on the front access

door of the test chamber. The phototube is mounted horizontally in a 41

X 76 X 98-mm (1.6 x 3.0 x 3.9-in) aluminum container which is open on

the top and bottom to allow for air cooling. The side adjacent to the

door glass is also open to provide for the collection of light from the

chamber. Aluminum foil is wrapped around the phototube with a 3.2-mm

(0.125-in) hole to admit the light. The elevation of the hole is 250 +

10 mm (9.8 + 0.4 in) above the top of the block. This is required to

prevent the phototube current from exceeding its operating limit. There

is no focusing so the phototube is exposed to a wide field of view as

’seen in figure 10. A toggle switch is used to turn the phototube circuit on and off. The output of the phototube is connected to one channel

of a high input impedance chart recorder, A 0.8 yF capacitance is

Certain commercial equipment, instruments, or materials are identified in

this paper in order to adequately specify the experimental procedure. In no case does such identification imply recommendation or endorsement by

the National Bureau of Standards, nor does it imply that the material or equipment identified is necessarily the best available for the purpose.

54
placed across the input terminals of the recorder to reduce fluctuations

in the phototube output. The second channel is connected to a time

marker circuit also shown in figure 10 which consists of a normally open

push button switch located on the lower front panel of the test cabinet

and wired in series with a 1.5-V battery. Figure 11 shows a phototube

and time marker record of time to flame attachment and time to fuel

contribution.

A. 5 Gas Supply

A toggle switch located on the front panel is used to actuate the

normally closed solenoid gas valves. Methane gas which is used for

producing the exposure flame is supplied from a gas cylinder to a pair

of 0 to 0.2 L/s (0 to 25 SCFH) rotometers with control valves at their

inlets where the gas flow rate is monitored and the exposure flame is

controlled. Nylon braid reinforced PVC tubing is used to feed the gas

from the flowmeter outlets to the solenoid valves. The tubing inside

diameter is 6.4 mm (1/4 in).

A. 6 Cooling Water

Cooling water is supplied to the test cabinet by 6.4 mm (1/4 in)

nylon reinforced PVC or equivalent tubing and it used for connecting the

cooling system inside the cabinet. All tubing connections are fitted

with hose clamps. The cooling water return line has a flow gauge which

indicates the water flow rate.

55
APPENDIX B COPPER DISK CALORIMETER

B. 1 Description

A copper disk calorimeter shall be used for measuring the total

incident heat flux received by the specimen surface in the ease of

ignition test apparatus. Basically, the calorimeter consists of two

blackened copper disks with thermocouples attached to their backs. One

unit is shown schematically at the top of figure 12. Their front surfaces are flush with the surface of a calcium silicate board of the same

size as the test specimens as seen in figure 13. The heat flux at the

locations of each copper disk is determined from its rate of temperature

rise. The thermocouple output voltages are fed to a chart recorder

which provides a record of the temperature histories.

The disks made of oxygen-free high purity copper are 3.2 + 0.03 mm

(0.125 + 0.001 in) thick and 19.1 + 0.2 mm (0.75 + 0.01 in) in diameter.

Chromel and alumel wires of 0.30 mm (0.012 in) diameter are attached to

the rear of the disk by peening the wires into individual 0.34-mm (0.0135-in)

diameter holes drilled 1 mm (0.04 in) deep and 6.4 mm (0.25 in) apart.

Each hole is to be 3.2 mm (0.13 in) from the center of the disk. This

provides an effective chromel and alumel thermocouple whose junction is

located within the disk. A brass bushing is made with an inside diameter

of 22.3 mm (7/8 in) and 1.6 mm (1/16 in) walls. It has a 3.2-mm (1/8-in)

flange on one end and three 1.2-mm (3/ 64-in) set screw holes on the

other. The holes are located 120° apart around the circumference and

56
set screws are used to support the disks flush with the end of the

bushing. The flange on the opposite end acts as a retainer that holds

the assembly in the correct position when it is placed in the calcium

silicate insulation board. Two pieces of 19.1-mm (3/4-in) thick board

are cut 140 mm (5.5 in) wide and 152 mm (6 in) high. Two 25.4-mm (1-in)

diameter holes are drilled through one board along the vertical centerline, centered 41 mm (1.6 in) from the top and bottom edges, respectively.

A 6.4-mm (1/4-in) diameter hole is drilled at each corner of both boards.

A portion of the second calcium silicate board is milled to provide

seating for the bushings and an exit channel for the thermocouple

wires. The bushings containing the calorimeter disks are placed into

the large holes and the boards are secured together by screws at each

corner. The function of the second, or backing, board is to lock the

bushings in position and prevent gas leaks around the discs. The thermocouple wires are brought out through the milled channel. Two thin even

coats of 3M flat black velvet paint^ are spray-applied to the front

surface of the calorimeter disks.

B. 2 Theory of Operation

The total heat flux is determined from the rate of temperature rise

of the copper disk using the equation

H = pzcT/a , (1)

^Certain commercial equipment, instruments, or materials are identified

in this paper in order to adequately specify the experimental procedure.

In no case does such identification imply recommendation or endorsement

by the National Bureau of Standards, nor does it imply that the material

or equipment identified is necessarily the best available for the purpose.

57
where a is the absorptivity of the black paint on the exposed surface

(0.97) specified by the manufacturer, p is the density of copper

3

(8960 kg/m ) , Z is the thickness, c is the specific heat of copper

(380 J/kg*K), and T is rate of temperature rise (°C/s) of the disk

(31.8 mm). It is assumed that the thermal conductivity is high enough

that the disk is at a uniform temperature. It is also assumed that

there are no heat losses from the specimen. This is approximately true

during the early stage of the exposure when the temperature rise is very

low. It is also important that the disk is supported in such a way as

to minimize the heat conduction through the supports. The operation is

shown schematically in figure 12.

The rate of temperature rise is determined from the slope of the

recorder trace using the relation

de ( 2 ) dT where — is the calibration constant of the thermocouple (24.6 K/mV) and

e is the slope (mV/s) of the linear portion of the recorder trace at the

beginning of the exposure.

Combination of (1) and (2) yields

u dT . , , . H = pzc e/a = ®e , (3)

pzc dT where <I> = — is the calibration factor which is calculated to be

a de

274 kW/m^*mV.

58
In order to ensure that the temperature measured is that of the

disk rather than that of a junction just outside, the thermocouple wires

are separated so that the junction is made inside the disc. The result

is a copper-alumel junction in series with a chromel-copper junction.

Since the temperature is the same for both junctions, the total voltage

produced is the same as that from a chromel-alumel thermocouple.

B.3 Heat Flux Measurement

In order to determine the total Incident heat flux exposure in the

ease of ignition apparatus, the following procedure is used;

A. Preheat the apparatus for 3 minutes with the calcium silicate

boards in the specimen holders.

B. Replace one board with the copper disk calorimeter.

C. Connect the calorimeter to a strip chart recorder and set the

span at 5 mV and the chart speed in the 1 to 5 second per inch

range.

D. Start the recorder.

E. Turn on the spark ignitor.

F. Turn on the gas.

59
G. Allow the exposure flame to burn for 8 to 10 seconds or until

the pen goes off scale.

H. Turn the gas off and allow the calorimeter to cool before

additional runs are conducted. (Cooling rate may be increased

by blowing air over the calorimeter disk.)

I. Measure the slope i in mV/s of the linear portion at the

beginning of the recorder trace. This slope should be constant

for several seconds in order to be regarded as a good run.

(See figure 14)

.

2 J. The total incident heat flux in kw/m is calculated using

equation 3 in section B.2.

60
NBS-114A (REV. 2 - 80 ) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

SHEET (See instructions) NBSIR 82-2503 July 1982

4. TITLE AND SUBTITLE

Development of an Ease of Ignition Test Using a Flame Exposure

5. AUTHOR(S)

J. R. Lawson and W. J. Parker

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)

Naval Sea Systems Command and Gypsum Association

10. SUPPLEMENTARY NOTES

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

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

bi bllography or literature survey, mention it here)

A test for the ease of ignition of interior finish materials by flame exposure was

developed. Two specimens, 140 mm (5.5 in) wide by 152 mm (6 in) high, face each

other at a distance of 53 mm (2.1 in) apart. A methane diffusion flame passes between their surfaces and extends to about 152 mm (6 in) above them. The operator

observes the specimen surface and records the time-to-flame attachment. A phototube,

which views the exposure flame, shows a marked increase in output when the specimens

start contributing fuel. The times-to-flame attachment were compared with the observed times of wall involvement in some full-scale tests. The ignition sensitivity

is expressed by the time-to-f lame attachment and by the time-to-fuel contribution.

The times-to-flame attachment measured in the ignition apparatus generally ranked

22 materials with the observed times of wall involvement in full-scale tests. The

results of this test may be useful as one factor in computer models of fire growth

in enclosures.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Building materials; fire tests; flame attachment; heat flux; ignition; room fires;

wall coverings

13. AVAILABILITY 14. NO. OF

Uni imited

1 1 For Official Distribution. Do Not Release to NTIS

PRINTED PAGES

64

pn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402. 15. Price

Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $9.00

USCOMM-DC 6043-P80
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