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NATL INST OF STANDARDS & TECH R.I.C.

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Babrauskaa, Vytenls/lgnltab^ty measure^ QC100 .U56 NO.86-3^5 1986 V19 C.1 NBS-P

REFERENCE

3445

NBS

PUBLICATIONS

Ignitability Measurements With the

Cone Calorimeter

Vytenis Babrauskas

William J. Parker

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1986

U.S. DEPARTMENT OF COMMERCE

“‘^ONAL BUREAU OF STANDARDS

-QC

ino

.1)56

8B-3445

1986

NBSIR 86-3445

IGNITABILITY MEASUREMENTS WITH THE

CONE CALORIMETER

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research

information CENTEH / , : -SC

Vytenis Babrauskas

William J. Parker

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1986

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 1

2. Design features desirable in an ignitability apparatus 2

2 . 1 Radiant heater 2 2.2 Spectral distribution of heating flux 2 2 . 3 Air flow rates 3 2.4 Means of ignition 4

2.5 Specimen size and thickness 4

3. Background for the development of the Cone Calorimeter 5

4. Detailed features and performance of the Cone Calorimeter 7

4.1 Radiant heater 7 4.2 Means of ignition 8 4.3 Specimen size 8

4.4 Specimen thickness 9 4.5 Air flow rates 10

4.6 Edge effects 10

5. Example Test Results 11

6. Comparison with empirical ignitability models 13

7. Comparison with detailed numerical models: Douglas fir 15

8. Additional specimen effects 17

9. Comparison with other test methods 19

10. Conclusions 20

11. Acknowledgements 21

References 22

iii
List of Figures

Page

Figure 1. General view of cone calorimeter 36

Figure 2. Detailed view of cone calorimeter (vertical orientation) 37

Figure 3. Variations in measured flux for actual specimen face at various

depths below the original level 38

Figure 4. Effect of specimen size on time to ignition [8] 39

Figure 5. Holder for fabrics for air- supported applications 40

Figure 6. Ignltability curves for various fabric/foam assemblies 41

Figure 7. Results for red oak and black PMMA 42

Figure 8. Black PMMA results compared to Hallman's results 43

iv
List of Tables

Page

Table 1. Effect of airflow on ignition times in the cone calorimeter 25

Table 2. White pine ignition times, showing effect of edge conditions.... 26

Table 3. Effect of specimen conditions on ignition times for

black PMMA 27

Table 4. Comparative behavior of commercial flexible

polyurethane foams 28

Table 5. Ignitability of air- supported fabrics 29

Table 6. Comparative ignitability results for red oak and black PMMA,

horizontal orientation 30

Table 7. Comparison of experimental PMMA results to simple

predictive rules 31

Table 8. Ignition times for Douglas fir particle board 32

Table 9. Effect of orientation on ignition times for aircraft panels 33

Table 10. Ignition of building materials determined by four

test methods 34

Table 11. Effect of ignition time on peak heat release rate 35

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Ignitablllty Measurements with the Cone Calorimeter

by

Vytenis Babrauskas

William J. Parker

Abstract

The Cone Calorimeter is a new- generation instrument developed

primarily for making rate of heat release measurements. This

instrument, containing a uniform and well-characterized irradiance

source, was also seen to be useful for making measurements of

radiant ignition on materials. Data have now been collected for a wide range of materials. The effects of various apparatus

dependencies are discussed. Also, some comparative data are available illustrating the performance of similar materials in

other apparatuses. Finally, for a selected material, Douglas fir

particle board, a detailed comparison with an ignition model has

been made

.

Key words; cone calorimeter; Ignitability ; plastics; radiant

ignition; upholstered furniture; wood materials

1 . Introduction

The Cone Calorimeter has now been in use several years and is becoming available at more research and testing laboratories. One of the measurements

available from it is radiant ignitability. In this paper, a review will be

made of: (1) the general problems of designing an apparatus to measure radiant

ignitability; (2) prior efforts in designing equipment for this purpose; (3)

the detailed features of the Cone Calorimeter, as applicable to ignitability

measurements; (4) the type of data obtained at the National Bureau of Standards (NBS) from the Cone Calorimeter; (5) a comparison between measured

ignitability values and predicted ones; and (6) a comparison to ignitability

data obtained using apparatuses of different design, at different laboratories.

1
2. Design features desirable in an ignitability apparatus

2 . 1 Radiant heater

The most important feature of a radiant ignition test is its heater. The

heater should be able to achieve adequately high irradiances , have a relatively

small convective heating component, present a highly uniform irradiance over

the entire exposed face of the specimen, and be designed so as not to change

its irradiance when the mains voltage varies, when heater element aging occurs,

or when the apparatus retains some residual heat from the exposure given to

prior specimen. A room fire burning near its maximum burning rate can show

temperatures over 1000 °C, producing corresponding irradiances of 150 kW/m^

Testing under such extreme conditions may not be required; nonetheless, if

ignition in post- flashover fires is to be simulated, irradiances of over 75

kW/m^ should be available, and preferably closer to 100 kW/m^ . A significant

convective component would negate the purpose of having a radiant ignition

test. Rather low convective fluxes can be achieved for specimens oriented

horizontally, face up, and with the prevailing air flow being upwards. VJhen a vertical specimen orientation is considered, it becomes evident that a boundary

layer will normally be expected to develop which will add some convective

component. A high uniformity of specimen irradiance should be strived for.

Here, a better uniformity can be expected under those conditions where the

convective component is minimized.

2.2 Spectral distribution of heating flux

The actual ignition source that can be expected will, in most cases, be a fire

in the vicinity of the target object. Its radiation spectrum will depend on the size of the fire. A very small fire can show a substantial fraction of its

radiation at wavelengths characteristic of H2 O, CO2 , and other combustion

products [1]. For larger fires - -certainly for room fires reaching a hazardous

condition- - the radiation from the soot tends to dominate; the result is an approximation to a grey body radiation [2]. For such a grey body radiation the

temperature will typically be in the vicinity of 1000 °C [3]. Experimentally,

2
heater choices for test apparatuses have included gas fired panels, electric

resistance heaters, flames, and high temperature lamps. Electrical heaters

tend to have a near-grey body characteristic and, assuming a dull or oxidized

surface condition, a high emissivity. Gas -fired panels derive a substantial

portion of their radiation from the ceramic face; thus, while there are discrete molecular wavelength peaks, overall the radiation shows a grey-body

continuum, typically in the range of 700 to 1000 °C temperatures [4] . High

temperature lamps, however, which have been used by several investigators [1,

5], typically have radiating temperatures of 2200 to 3000 °C. The spectral

distribution of such a source is much different from one operating at 1000 °C.

Whether this change in spectral characteristics is important depends on the

surface of the material to be ignited. For a material with a radiant absorptance independent of wavelength, this source variation would not matter.

Hallman, however, has reported data for a large number of plastics, which show

that while there are some specimens with negligible wavelength dependence to

their absorptance, the majority show strong variations [1]. Hallman also made

measurements of ignition times of plastics with both a flame source and high

temperature lamps . The effect on ignition times ranges from negligible to more

than an order of magnitude, depending on the specimen. For a general purpose

radiant ignition test, flames would probably be the least desirable source of

heating. For a bench- scale test the size of flames has to be kept small. This

means that such flames are optically thin, their emissivity is low and the

higher heat fluxes could not be achieved unless a strong convective component

were added.

2.3 Air flow rates

It is known that air flow rates can influence the times to ignition, especially

that excessive air flow rates can give increased ignition times. One interpretation of this kind of observation is that the phenomenon of ignition can be

visualized as the reaching of the lower limit of flammability in the volume of

pyrolysates near the specimen surface. High air flow rates tend to dilute this

volume and, thus, delay ignition. Another explanation is that the increased

air flow simply cools the specimen and reduces its rate of pyrolysis.

3
Systematic guidance in this area is not available. However, as an example of

the effect of air flow, measurements have been made in the OSU apparatus [6].

Specimens of black polymethylmethacrylate (PMMA) were exposed in the horizontal

orientation to a heating flux of 35 kW/m^ . With an air flow of 12 2/s through

the combustion chamber, the ignition time was 209 s. When the air flow rate was doubled to 24 i/s, the specimen ignition time went up to 403 s.

2.4 Means of ignition

In some cases no external ignition source is desired, and specimen testing is

to be done solely on the basis of auto- ignition. In most cases, however, an external ignition source is desirable. This ignition source should, in

general, not impose any additional localized heating flux on the specimen.

Apparatus designs have been developed [e.g., 6] with impinging pilots, which can in some cases produce such high localized heat fluxes as to burn a hole

through the specimen at the point of impingement, yet not ignite it outside of

that region. Applications for such devices would tend to be specialized, since

the general objective of radiant ignition testing is to produce data which can be analyzed in the context of an assumed one-dimensional heat flow. The

ignitor should reliably ignite a combustible gas mixture in its vicinity.

Thus, the location of the ignitor must be chosen so that it is near the place

where maximum evolution of pyrolysate gases is expected. Some materials are highly fire-retardant treated, and, when heated, emit vapors which tend to

extinguish a pilot flame. The ignitor has to be designed so as not to be

extinguished by fire-retardant compounds coming from the specimen, nor by air

flows within the test apparatus.

2.5 Specimen size and thickness

Both specimen area and thickness may be expected to have some effect on the

ignitability . Simms [7] has studied in some detail the general problem of area effect on ignition. The effect is seen to be smaller when irradiances are high

than when they are low. The exact magnitude of the effect is also dependent on the specimen's thermophysical properties. For specimens 0.01 m^ or larger,

however, the Increase in ignition time is typically only 10% or so over what

4
would be seen with a specimen of infinite area. The main practical size and

thickness limitations come from the fact that the specimens to be tested should

exhibit primarily one -dimensional heat transfer; thus, the configuration

should be such that excessive edge effects are not seen. If the specimen

thickness is such that it is thermally thick (the heat wave penetration depth

being less than the physical depth) , then further increases in thickness are not expected to change ignitabllity results. For thinner specimens, however,

there can be expected to be a thickness effect, and the backing or substrate

material's thermophysical properties can be of importance.

3. Background for the development of the Cone Calorimeter

Early ignitability testing was generally based on a furnace exposure to

determine an ignition temperature, an example being the Setchkin furnace,

developed in the late 1940 's [8]. Later, concepts such as ignition by flame

impingement were investigated [9]. Testing for radiant ignitability is a relatively new approach. It is motivated by the current understanding of the

physics of room fire development, where the imposed radiant flux is among the

most important of quantities. Radiant ignitability has been a part of the Ohio

State University (OSU) test [6], although in operation there, an impinging

pilot is usually superimposed.

The ISO (The International Organization for Standardization) ignitability

apparatus, under development since the early 1970 's [10] represented the first

widely used apparatus specifically designed for testing radiant ignitability.

That apparatus, even in its earliest form, contained an especially appropriately designed thermal radiation source in the form of a truncated cone. This

design eliminated the difficulty with most conventional designs, namely, that

the specimen center is heated more than the edges. For ignitability measurements, this was the main advantage for this heater geometry.

A few years later, at the National Bureau of Standards (NBS) , following

experiments with a number of heat release rate apparatuses, both standard and

5
unique, it was desired to develop a new instrument which, while still economically affordable for commercial testing laboratories, would alleviate most of

the known difficulties of existing instruments. A significant shortcoming of

many of the existing designs that were capable of operating to high fluxes was that specimen irradiance uniformity tended to be poor. The geometry of the ISO cone in the ignitability apparatus appeared to be ideal for use also within a heat release rate apparatus. The apparatus, as developed at NBS using the

conical heater (Figures 1 and 2), became known as the Cone Calorimeter, and has

been described in detail [11,12]. This apparatus has been put forth by the

American Society for Testing and Materials (ASTM) as a proposed standard [13].

Used in the Cone Calorimeter, the conical shape of the heater was seen to have

additional advantages; it allowed the flame to exit the apparatus directly,

when used in the horizontal orientation (the Cone Calorimeter, unlike the ISO

cone, is designed to also be usable with a vertical specimen and cone orientation) , and it provided a geometry which deflected the flame plume in such a manner that a cold air sheath kept the combustion products from directly

Impinging on the heater elements. In addition to the ability to test in both

orientations, the Cone Calorimeter cone was designed with a different heating

element and different mechanical layout details, which permit measurements to

be made at irradiance of up to 110 kW/m^ , instead of being restricted to 50

kW/m^ , as is specified for the ISO cone.

A number of other features serve to differentiate the Cone Calorimeter from the

ISO ignitability apparatus, in addition to the obvious one of being able to

make heat release, mass loss, and smoke measurements. The ISO ignitability

apparatus uses a specimen 165 mm by 165 mm, which is exposed only at a circular

opening of 140 mm diameter in the center. This is not objectionable, per se . for ignitability purposes alone, but for heat release rate testing would not be

desirable since the difference between actual surface area and radiatively

exposed surface area would be substantial. The specimen holder in the Cone

Calorimeter was designed so that there is only a very small, 3 mm, lip around

the face of the specimen. Finally, the piloting arrangements are of a very

different nature.

6
4. Detailed features and performance of the Cone Calorimeter

4.1 Radiant heater

The radiant heater in the Cone Calorimeter is a wound resistance heating

element, covered by an Incoloy* sheath. After a short period of conditioning

the heater sheath assumes a dark, dull appearance. Measurements indicate [11]

that the heater behaves as nearly an ideal black body, with an emissivity x view factor product of 0.85, and the effective emissivity approaching unity.

This means that the spectral distribution is likely to be very close to that

expected from room fires.

The uniformity of the heating flux over the face of the specimen in the Cone

Calorimeter has been described [11]. Over the range of irradiances from 25 to

100 kW/m^ , the ratio of the flux at the specimen center to average flux varied

only from 1.00 to 1.06. The peak deviations from average were typically 2% in

the horizontal orientation and 7% in the vertical. (Deviations are, perforce,

higher in the vertical orientation, since the effect of convective fluxes is

more pronounced there.) Additional measurements have been made in the specimen-depth plane. This has been a special concern to the designers of the ISO

apparatus, where a special compressive loading mechanism is provided which

attempts to re -level the exposed surface, in case the specimen recedes due to

melting. In the Cone Calorimeter, measurements have been made in the horizontal orientation using a small, 6 mm diameter Garden- type heat flux gage. A

flux mapping was obtained starting at the initial surface, and progressing down

to the maximum depth of a specimen, which is 50 mm. A normal aluminum foil

rectangular specimen wrap was used for these tests, but without any specimen.

The results (Fig. 3) show that at heating fluxes of both 25 and 50 kW/m^ the

deviations over the entire specimen depth are less than 10%, and can, therefore, be neglected.

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.

7
4.2 Means of ignition

The ISO apparatus was designed with a "dipping" gas pilot, which is periodically thrust for a short while down close to the specimen face, then retracted.

This solution, however, introduces an uncertainty into ignition times and

provides further complexity. A gas pilot, in our experience, also requires

oxygen premix to be used if a flame which is both small and resistant to

blowout is to be achieved [14]. With highly fire-retardant-bearing products, even such precautions are not likely to lead to a reliable pilot; thus, for

instance, the ISO apparatus uses a second pilot to reignite the main pilot.

Pilot stability also tends to be crucially dependent on the physical condition

of the pilot tube tip, and significant maintenance can be necessary. Finally,

if used in a heat release apparatus, a gas pilot would also serve to add noise

to the baseline of the heat release measurement. Initial experience at NBS

with a more tractable alternative- -electric spark ignition- -was obtained with

the NBS -II calorimeter [15], where a spark plug arrangement was provided for

ignition. This development was successful, and so a similar electric pilot was designed for the Cone Calorimeter. When testing in the horizontal orientation,

the spark plug gap is located 13 mm above the center of the specimen; in the

vertical orientation, the spark plug gap is located at the specimen plane and 5 mm above the top of the specimen holder.

4.3 Specimen size

In addition to the investigation by Simms, cited above, Nussbaura and Ostman

[16] have studied the ignition of specimens in an experimental apparatus

patterned after the Cone Calorimeter, but accommodating 200 by 200 mm specimens. Their comparison of the ignition times of these larger specimens

against the standard 100 by 100 mm ones (Fig. 4) shows that quadrupling the

specimen area decreases the ignition time by about 20%. Thus, there is a scale

effect, but the scale effect is not very large.

8
4.4 Specimen thickness

The Cone Calorimeter is intended for testing actual commercial products. Thus

the specimen thickness should be, as much as possible, the thickness of the

finished product. There are limitations at both end of the scale, however.

The instrument is restricted to testing specimens not thicker than 50 mm. For

products which in their finished state are greater than 50 mm thick, it can readily be seen that for almost any realizable combination of thermophysical

properties and incident radiant fluxes, a 50 mm specimen is thermally thick,

and increasing thickness would not change the ignition times [17,18]. By

making calculations for various densities and heat fluxes using the model to be

described below, it was found that for particle board the minimxim thickness

required to insure that the specimen is thermally thick can be represented by:

i = 0.6 p/q" (1)

where i is the thickness (mm) , p is the density (kg/m^ ) and q" is the

heat flux (kW/m^ )

. This is probably a reasonable rule of thumb for other

materials as well. The proportionality of the required thickness to p/q" is

derived from classical heat conduction theory by equating the time for the

front surface to reach the ignition temperature to the time for the rear

surface temperature to begin to rise and assuming that the thermal conductivity

is proportional to the density. Numerical calculations were necessary to

determine a suitable constant because of the impact of the front surface heat

losses

For materials which are not thermally thick at the time of ignition the nature

of the backing material or substrate can influence the measured value of the

ignition time. ^n the cone calorimeter the substrate is a blanket of refractory ceramic fiber material, having a nominal density of 65 kg/m^ . In use, the

material assumes a more compacted density of roughly 100 kg/m^ . Whenever

possible, materials, whose thicknesses are less than the minimum suggested in

the above formula, should be mounted on that substrate material over which they

9
will actually be used. As a practical guide for testing unknown conunercial

samples, it is desirable to specify that any specimens less than 6 mm thick

should always be considered as needing to be tested over their in-use substrate .

Fabrics are a special case. Thin fabrics are sometimes used for constructing

air- supported structures; these should be tested with an air space in back,

simulating the usage conditions. A special holder has been constructed (Fig.

5) which allows the fabrics to be pulled taut and held above a dead air space.

4.5 Air flow rates

In the Cone Calorimeter, air flow experiments have been done with two types of

materials, black PMMA and redwood. The results are listed in Table 1. The

conclusion is that over the complete feasible air flow range, from zero (which

of course would not be practical for operation) , through the normal value of 24

i/s [13], up to the apparatus maximum of 41 i/s, the effects of air flow rates on ignition times in the Cone Calorimeter are very minor. Since the thermoplastic PMMA material and the charring redwood represent very different types

of degradation behavior, it is expected that these conclusions have some generality.

4.6 Edge effects

In the vertical specimen orientation, the specimen has to be restrained against

falling out; thus, the vertical specimen holder incorporates a small lip

covering 3 mm along the edges. In the horizontal orientation, no special

measures need to be taken against falling out. Thus, for many types of speci- mens it is satisfactory to simply cover the edges and bottom with a piece of

aluminum foil, leaving the top exposed in its entirety. For wood specimens,

however, the ignition time can be substantially reduced by edge ignition. For

pyrolysis occurring near the edge, the volatiles can flow more easily along the

grain and then exit along the edge. When the specimen edge is covered with

aluminum foil, stopping flush with the specimen face, the products are forced

out through the narrow passage between the edge of the wood and the foil layer.

10
thus causing a high fuel concentration at the surface allowing for earlier

ignition. Once a flame is formed it can propagate rapidly to involve the whole

surface. This problem is alleviated by using a stainless steel edge frame for

the horizontal orientation, which, same as the vertical holder, provides a 3 mm

lip around the edge of the specimen face.

Table 2 gives the results for white pine specimens, 20 mm thick. In most cases

the times to ignition is substantially shorter when no edge frame is used. The

times to ignition in the vertical orientation are also much greater than in the

horizontal. This effect will be discussed further below.

An additional specimen preparation technique that has been found of use for

heat release rate testing is to cover the sides of a (horizontal) specimen with

some slow-burning material. This allows the closest approach to an ideal

burning manner whereby the specimen surface would regress down uniformly. For

PMMA this is possible by gluing cardboard strips, approximately 0.5 mm thick,

to the edges. This might, in principle, affect the ignition times. Data in

Table 3, however, suggest that the effect is negligible, at least for PMMA.

5. Example Test Results

During the last few years, ignition data have been obtained from a large number

of materials tested in the Cone Calorimeter. For an example, a series of

flexible polyurethane foam materials have been tested, where four specimens of

similar density and physical properties were tested; two were fire-retardanttreated formulations and two untreated ones. The data (Table 4) show rates of

heat release which are very similar for all specimens. The ignition times,

however, are not different. At an irradiance of 25 kW/m^ the treated foams

took 3 to 8 times as long to ignite, compared to the untreated ones. When the

irradiance was raised to 50 or 75 kW/m^ , however, these differences shrank to a factor of two or less. This is consistent with the observation that the

typical fire retardants added to polyurethane foams can make them resistant to

very small ignition sources, but that the ignition and burning rate behavior is

11
essentially unchanged when larger ignition sources are used [19]. These data

are for furniture foams alone.

A more extensive investigation was made of foam/fabric composites, representing

specimens taken from upholstered furniture. Figure 6 gives these results. The

list of specimens encompasses the whole range of expected furniture fire

behaviors- -a wool/neoprene specimen typically shows the most fire-resistive

possible behavior available with commercial materials, while an unretarded

(NFR) polyurethane foam, covered with a polyolefin fabric shows among the least

fire resistive behaviors. Various fire retarded combinations (FR) are intermediate. A sufficient number of tests was made to characterize the complete

ignitability curve, including the determination of the minimum irradiance

required to achieve piloted ignition (limit irradiance). It is striking to

note that the range of variations in ignitability for this wide range of

materials is very small, about a factor of 2 to 3. This small range of

behavior is most likely due to the fact that the effective density of the test

material is a dominant factor in determining its ignitability. For furniture

applications, the range of acceptable densities is rather small.

Tests have also been conducted on fabrics intended for air- supported buildings.

These fabrics include an impermeable coating, which is typically polytetrafluoroethylene , silicone, or PVC . These were tested using the holder illustrated in Figure 5. Table 5 gives the results for two irradiances - - 35 kW/ra^

chosen to represent the typical peak heat fluxes from limited ignition sources

[19], and 75 kW/m^ , which can represent heat fluxes in a flashed-over room. It can be seen that a satisfactory discrimination can be made between materials

likely to ignite from a limited fire, and ones which would get involved only in

the event of a fully flashed-over room fire.

Data have also been obtained on red oak, which has often been used as a standard calibration material. Table 6 gives these results over a wide range

of irradiances; also given are the comparative results for black PMMA, which

is being considered for use as a standard calibration material, representing

simply pyrolyzing, non-melting plastics. Figure 7 shows plots of both sets of

results on a log-log scale. It can be seen that for irradiances of 50 kW/tn^

12
and greater, a power law can be fit very well to the results for both materials. It shows a dependence of the ignition time on approximately the -1.9

power of the irradiance for red oak and the -1.7 power for PMMA.

6. Comparison with empirical ignitability models

PMMA is a convenient combustible to use in ignitability studies and has been

examined by other investigators. The most systematic work is that due to

Hallman [1]. Hallman investigated black PMMA in a thickness of 12.7 mm using

an apparatus where a vertical specimen could be exposed to the irradiance of

either benzene flames or tungsten lamps. His results are shown in Figure 8,

along with the Cone Calorimeter results shown in Figure 7. First, it can be

noted that since black PMMA has a radiant absorptance of 0.92 to 0.96, essen- tially independent of wavelength [1]

that source wavelength variations would

not be expected to influence the results; this is borne out by the data of

Figure 8. Hallman's data show a power- law dependence, on the average, of -2.0.

It is quite striking that the agreement between the Cone Calorimeter and the

Hallman data is so good, since the apparatuses are totally dissimilar.

Since PMMA is a material for which the thermophysical properties are known, it

is possible to make a theoretical analysis. The simplest analysis would be

based on the assumption that the solid is inert, semi- infinite in thickness,

originally at a uniform temperature T^^ , and then at time t = 0 it starts to be

heated with a radiant flux q" . The actual specimen pyrolysis is ignored, and,

instead it is assumed that ignition occurs when the specimen's exposed face

reaches

^

, its ignition temperature. The solution for the ignition time is

then [ 20 ]

t. =7 (kpC)(T. -T )^(a q")'^ (2) ig 4 ig o

^

For PMMA [21] it is appropriate to assume that a = 0.95, T^^ = 636 K, and that

kpC, the product of the thermal conductivity x density x heat capacity is 0.346

s • (kW/m^

Substituting these values for PMMA gives

13
= 0.346x10^ q""^ (s) (3)

The above solution would assume that there is no convection or reradiation.

The former is a reasonable assumption at all except very low fluxes. The

latter, however, is not reasonable. The reradiation term is proportional to

aaT^ , where a is the Stefan-Boltzmann constant and T^ is the specimen surface

temperature. This starts out at T^ when t = 0 and goes to T^

^ at t = t^^

. The

reradiation term can be incorporated into the heat conduction equation;

unfortunately, the equation then no longer possesses an analytical solution.

For estimation, one can set T^ at the fixed value of T^

^ for all times. The

expression for PMMA then becomes

Hallman considered, instead, a number of somewhat more complex models, but did

calculational use, he proposed an empirical relationship, based on fitting all

of his plastics data, of which PMMA was only a small portion. His recommendation, in the same units as above, is that

t.g = 0.346x10= (q" - 9.28)’2 (s) ( 4 )

not use them when he found poor agreement with his data. For practical

1.04

(kpC)

0.75

t

(5) ig

2 (aq")

When evaluated for PMMA using the same properties as above, this gives

t.g = 2.22x10= q"-2 (s). ( 6 )

14
Both of the above relationships are evaluated in Table 7. Neither is particularly good at representing the experimental data closely. It is interesting to

note that Hallman's expression (Eq. 6) does not represent his data any better

than does Eq . 4. This is presumed to be because his correlation was optimized

as the best fit for all of the plastics tested, and not just for PMMA. To

achieve better predictive results , it is clear that a more advanced model of

ignition is needed.

7. Comparison with detailed nximerical models: Douglas Fir

Ignitability is but one of the responses of a material to a fire exposure. A

numerical model for the total fire response of wood was developed by Parker

[22]. This model includes heat release rate, surface temperatures, and mass

loss rate predictions. The heat release rate is determined by integrating the

product of the instantaneous mass loss rate and the instantaneous heat of

combustion at each depth over the thickness of the exposed wood slab. When the

calculated heat release rate reaches the minimum required to maintain a flame

on the surface, ignition is assumed to occur. Prior to that time the heat

release rate is set equal to zero. This minimum flux is taken to be 30 kW/m^ . The model takes into account the degree of char, the char shrinkage and the

variation in thermal conductivity, specific heat and density with the temperature. It also accounts for thermal radiation and convective cooling from the

front surface. The surface is assumed to be black for both absorption and

emission of thermal radiation. The model was initially checked out with

Douglas fir particle board. In this case it was assumed that the kinetics were

governed by a single first order reaction. The activation energy, frequency

factor, heat of combustion of the volatiles, char contraction factors, and the

thermal conductivity were all experimentally determined on specimens taken from

the same batch of material as those tested in the cone calorimeter. The

calculated and measured heat rates have been examined in detail earlier [22].

The ignition times of Douglas fir particle board were measured in the cone calorimeter at incident radiant heat fluxes of 25, 50, 75 and 100 kW/m^ using

vertically oriented specimens . The calculated ignition times were taken to be

15
equal to the times of appearance of a calculated heat release rate of 30 kW/m^

These times are compared in Table 8. Since there is some question on the

applicability of the equation for convective cooling based on steady state

laminar free convection, calculations are also included for the case where the

convective cooling is assumed to be equal to zero. Thermal radiation from the

surface is included in both cases. The calculated temperature at the calculated time to ignition is included for all of the entries in the table.

In a classic paper by Bamford, Crank and Malan [23] in 1945 it was reported

that a minimum mass flux of 2.5 g/m^ was required to sustain flaming combustion

of wood. This ignition criteria was applied to the calculated mass loss rates

to obtain another set of ignition times in Table 8, also with and without

convective cooling at the surface.

Quintiere and Harkleroad [24] deduced an ignition temperature of 380 °C for

Douglas fir particle board. The times at which the calculated front surface

temperature reaches this 380 °C is also included in Table 8 with and without

convective cooling at the surface.

Table 8 it shows that the predictions from the model are encouraging. The

minimum mass flux criteria along with the assumption of no convective cooling

from the surface is slightly better than the others in accounting for the

experimental values. However, it would be premature at this point to argue

that the difference is significant. The model is quite good at higher fluxes,

but all of the criteria predict a significantly longer time to ignition than was observed at an incident flux of 25 kW/m^ . Although the reason for this

disagreement is not understood, some possibilities to explore include: (1)

oxidative pyrolysis at the surface which is exothermic and more rapid; (2)

local effects due to variation in properties along the surface associated with

the annual ring structure, fissure development, etc.; and (3) inadequate data on the thermal conductivity of char at high temperature. The model assumes no reaction with oxygen at the surface and assumes the heat transfer to be one dimensional. Measurements of the thermal conductivity could only be carried

out up to 270 °C. Beyond that point the data were extrapolated. The assumption of a single first order reaction may not be adequate. It should also be

16
noted that lot- to -lot variations among wood products can have a strong effect

on ignitability measurements. Quintiere and Harkleroad [24], studying Douglas

fir particle board from a different lot, found ignition times of 150 s at 25

kW/m^ and 30 s at 50 kW/m^

.

The model assumes average properties and heat fluxes over any plane parallel to

the surface. While this is necessary to predict the average heat release rates

which are actually measured in the cone calorimeter, points of locally high

heat fluxes or locally low density are where ignition is likely to be initiated. In order to provide some indication of the magnitude of these effects

the ignition times were calculated for a 10% higher flux and for a 20% lower

density. Parts of the surface may pass through the lower density spring growth

while other parts are passing through the more dense summer growth. Increasing

the flux from 25 to 27.5 kW/m^ dropped the calculated ignition time from 143 to

114 seconds. Dropping the density from 709 to 567 kg/m^ , while maintaining the

incident radiant flux at 25 kW/m^ , reduced the ignition time from 143 to 125

seconds. These calculations were based on the minimum mass loss criterion

assuming no convective losses from the surface. For heat fluxes approaching

the critical radiant flux for ignition of the material, the ignition times

become more sensitive to these variations in heat flux and density and also to

any uncertainty in the actual value of the heat flux which may have an error of

up to 5%. These effects provide possible explanations for the poor agreement

at 25 kW/m^

.

8. Additional specimen effects

Specimen orientation . This is a potentially important effect. It should not

be considered an apparatus dependency, per se . since various specimen orientations can occur in real fires, and it is desirable to represent them in a test.

Thus, the Cone Calorimeter has been designed with two orientations, vertical,

and face-up horizontal to represent at least the major possible configurations.

Tables 1, 2, and 3 show that orientation makes little difference for PMMA and

for redwood. For white pine, however, the horizontal orientation ignition

times were consistently shorter than the vertical ones. This effect was also

17
noted by Atreya ^

al. for mahogany specimens [25]. Kashiwagi has also studied

orientation effects, although only in an auto- ignition mode. He found [26]

that, for that mode, the horizontal orientation ignition times were shorter

than the vertical ones for both PMMA and red oak specimens. The interpretation

of the results for wood specimens is especially difficult to provide, partly

because the ignition of wood can be influenced substantially by its surface

roughness conditions, and the test specimens are normally not characterized for

this property.

Additional comparative data have been obtained on a series on aircraft cabin

wall panel materials [27]. These are types of specimens are difficult to

ignite and might be expected to show substantial variations. Table 9 shows the

results. The variations do not appear to be significant, except that at the

highest tested irradiance , 75 kW/m^ , ignition is marginally slower in the

vertical orientation.

Finally, comparative orientation data from an inter- laboratory comparison of

building materials (discussed below) are also shown in Table 10. In this

series, the ignition times for the horizontal orientation, with one exception,

are shorter than in the vertical orientation. This may suggest that, in

general, it is somewhat easier to achieve the requisite lower flammability

limit above a burning pool, than it is in the thinner, higher velocity boundary

layer which results in the vertical orientation. On the other hand the

convective cooling of the horizontal specimens is less than it is for the

vertical specimens so that the same surface temperature is reached earlier for

the horizontal specimens.

Relation to heat release Not much exploration has been done on the relationship between time to ignition and the rate of heat release. In general, it can

be expected that these are not highly correlated properties. In at least one situation, however, a significant correlation can be seen. White pine speci- mens were tested for ignitability and rate of heat release. The data in Table

11 show that at higher irradiances ignition time data exhibit little scatter,

and there is no correlation to heat release rate. At an irradiance of 20

kW/m^ , however, the ignition is very slow and there is a large amount of

18
sample- to -sample variation. Under those circumstances an inverse relationship

can be seen between the ignition time and the peak value of the heat release

rate. The correlation in Table 10 may possibly be explained on the basis of a delayed ignition allowing a larger accumulation of combustible vapors, which

when ignited, give rise to a larger peak heat release rate (wood materials

specimens generally show the peak rate of heat release just shortly after

ignition). In a general case, for natural products, ignition and heat release

rate variability can be attributed to specimen density variations [28]. In the

present series, however, the specimen density variations were less than 3%

among the specimens

.

9. Comparison with other test methods

A series of materials was procured by the Swedish National Testing Laboratories

(Statens Provningsanstalt) for use in test standardization. Tests were conducted at NBS in the Cone Calorimeter. Ostman, Svensson and Blomqvist [29]

provided data taken in three other ignition apparatuses: the ISO ignitability

test, the OSU apparatus, and a radiant panel test devised by the STFI (Swedish

Forest Products Research Laboratory) . Some of the relevant test parameters

were

:

Cone Calor. ISO OSU STFI

Specimen size (mm)

Orientation

Air flow (i/s)

Pilot

100 X 100

H,V

24

electric

165 X 165

H

N.A.

dipping

150 X 150

V

11

gas

,

non- impinging

150 X 150

V

20

gas

,

non- impinging

The results are shown in Table 10. It is clear that ignition times, as measured in the Cone Calorimeter, are faster in the horizontal orientation than

in the vertical. In general, when times to ignition are ordered, the following

approximate trend may be seen:

19
longest

shortest

STFI - -vertical

ISO- -horizontal

Cone- -vertical

OSU- -vertical

Cone- -horizontal

Generally there is a broad range of agreement between the different methods for

most of the materials tested, although there are some apparent outliers. The

differences between the methods may not necessarily be statistically significant, however; this should be addressed in a future study. Most of the dense

materials, such as particle board, medium density fiberboard, spruce wood,

gypsum board, and paper wall covering on particle board, show ignition time

results which do not exceed more than a range of 2:1 among the test methods.

It is interesting to note that these are all cellulosic products. The remaining specimens, including both the foams, show one or more apparent outliers.

This is not unexpected, since foam specimens can melt, shrink, or recede from

the surface, prior to ignition. These types of behavior are not typically

encountered with cellulosic specimens. Melamine-composite specimens are a special case, since they have a tendency to explosively delaminate instead of

igniting uniformly over the surface; thus, characterizing such specimens with

an ignitability test may not be appropriate.

10 . Conclus ions

The Cone Calorimeter allows the collection of radiant ignition data over a wide

controlled range of irradiances . It is operable in two orientations, the

choice of orientation being determined by the product application category.

The piloting mechanism has been developed in response to known difficulties of

other apparatuses and functions reliably. Radiant ignition data can be

correlated very approximately by power law functions; this fit is better at

higher irradiances. More detailed modeling of the thermal degradation a particular specimen type can result in improved model fitting. When data are compared to other ignitability test apparatuses, it is seen that agreement

among various test methods is better for higher density products than for

plastic foams and other low density materials.

20
11 . Acknowledgements

W. H. Twilley and G. L. King conducted the laboratory experiments and reduced

the test data.

21
References

[1] Hallman, J.R., Ignition Characteristics of Plastics and Rubber. Ph.D.

Dissertation. Univ. of Oklahoma, Norman (1971)

[2] Hagglund, B., and Persson, L-E., The Heat Radiation from Petroleum Fires,

FOA Rapport C 20126-D6(A3) . Forsvarets Forskningsanstalt , Stockholm

(1976) .

[3] Babrauskas , V., Estimating Large Pool Fire Burning Rates, Fire Technolo19, 251-261 (1983).

[4] Comeford, J.J., The Spectral Distribution of Radiant Energy of a GasFired Radiant Panel and Some Diffusion Flames, Comb . and Flame . 18 . 125-

132 (1972).

[5] Tewarson, A., Physico-Chemical and Combustion/Pyrolysis Properties of

Polymeric Materials (NBS-GCR-80-295) , [U.S.] Nat. Bur. Stand. (1980).

[6] Standard Test Method for Heat and Visible Smoke Release Rates for

Materials and Products, ASTM E906 , American Society for Testing and

Materials, Philadelphia.

[7] Simms, D.L., Ignition of Cellulosic Materials by Radiation, Comb . and

Flame . 4, 293-300 (1960).

[8] Setchkin, N.P., A Method and Apparatus for Determining the Ignition

Characteristics of Plastics, J.

^ Research of The National Bureau of

Standards . 43 . 591-608 (1949).

[9] Parker, W.J., The Development of a Test for Ease of Ignition by Flame

Impingement, Report 10495, [U.S.] Nat. Bur. Stand. (1971).

[10] Fire tests -- Reaction to Fire -- Ignitability of building products,

Draft International Standard, ISO/DIS 5657, International Organization

for Standardization (1985).

[11] Babrauskas, V., Development of the Cone Calorimeter- -A Bench-scale Heat

Release Rate Apparatus Based on Oxygen Consumption, Fire and Materials . 8, 81-95 (1984).

[12] Babrauskas, V., Construction Drawings for the Cone Calorimeter, [U.S.]

Nat. Bur. Stand. (1985).

[13]

Proposed Test Method for Heat and Smoke Release Rates for Materials and

Products Using an Oxygen Consumption Calorimeter, Annual Book of ASTM

Standards, Vol. 04.07, American Society for Testing and Materials (Nov.

1986) .

22
[14] Babrauskas , V., Combustion of Mattresses Exposed to Flaming Ignition

Sources, Part II. Bench-scale Tests and Recommended Standard Test (NBSIR

80-2186). [U.S.] Nat. Bur. Stand. (1980).

[15] Tordella, J.P., and Twilley, W.H. , Development of a Calorimeter for

Simultaneously Measuring Heat Release and Mass Loss Rates (NBSIR 83-

2708). [U.S.] Nat. Bur. Stand. (1983).

[16] Nussbaum, R. , and Ostman, B., Larger Specimens for RHR Tests in the Cone

Calorimeter (ISO TC92/SDC1/WG5 N.59). Trateknik Centrum, Institutet for

Trateknisk Forskning, Stockholm (1985).

[17] Weatherford, W.D., Jr., and Sheppard, D.M., Basic Studies of the Mechanism of Ignition of Cellulosic Materials, Tenth Svmp . ( Inti . ) on Combus

tion, pp . 897-910. The Combustion Institute (1965).

[18] Wesson, H.R., Welker, J.R., and Sliepcevich, C.M., The Piloted Ignition

of Wood by Thermal Radiation, Comb, and Flame . 16 . 303-310 (1971).

[19] Babrauskas, V. , and Krasny, J.F.

Fire Behavior of Upholstered Furniture . NBS Monograph 173, [U.S.] Nat. Bur. Stand. (1985).

[20] Carslaw, H.S., and Jaeger, J.C., Conduction of Heat in Solids . Clarendon

Press, Oxford (1959).

[21] Modak, A.K., and Croce, P.A., Plastic Pool Fires, Comb, and Flame . 30 . 251-265 (1977).

[22] Parker, W.J., Development of a Model for the Heat Release Rate of WoodA Status Report (NBSIR 85-3163). [U.S.] Nat. Bur. Stand. (1985).

[23] Bamford, C.H., Crank, J. and Malan, D.H., The Combustion of Wood. Part I,

Proc . Cambridge Phil. Soc . 42 . 166 (1946)

[24] Quintiere , J.Q. and Harkleroad, M. , New Concepts for Measuring Flame

Spread Properties (NBSIR 84-2943). [U.S.] Nat. Bur. Stand. (1984).

[25] Atreya, A., Carpentier, C., and Harkleroad, M. , Effect of Sample Orientation on Piloted Ignition and Flame Spread, pp . 97-109 in Fire Safety

Science -

Proceedings of the First International Symposium . C.E. Grant and

P.J. Pagni , eds .

Hemisphere Publ., Washington (1986).

[26] Kashiwagi, K. , Effects of Sample Orientation on Radiative Ignition,

Combustion and Flame . 44 . 223-245 (1982).

[27] Quintiere, J.G., Babrauskas, V., Cooper, L. , Harkleroad, M. , Steckler,

K. , and Tewarson, A. , The Role of Aircraft Panel Materials in Cabin Fires

and Their Properties (DOT/FAA/CT- 84/30) . Federal Aviation Administration, Atlantic City (1985)

23
[28] Chamberlain, D.L., Heat Release Rate Properties of Wood Based Materials

(NBSIR 82-2597) . [U.S.] Nat. Bur. Stand. (1983).

[29] Ostman, B., Svensson, I.G., and Blomqvist, J., Comparison of Three Test

Methods for Measuring Rate of Heat Release, to appear in Fire and

Materials

24
Table 1. Effect of airflow on ignition times in the cone calorimeter

Material Thickness (mm) Orientation Fan Setting Ignition time^ (s)

PMMA 13 horizno fan 71

PMMA 13 horiz24 i/s 76

PMMA 13 horiz41 i/s 67

PMMA 13 vert

no fan 86

PMMA 13 vert

24 i/s 84

PMMA 13 vert

41 i/s 77

redwood 13 horiz

no fan 23

redwood 13 horiz

24 i/s 24

redwood 13 horiz

41 i/s 31

redwood 13 vert

no fan 22

redwood 13 vert

24 i/s 27

redwood 13 vert

41 i/s 29

® - - at an irradiance of 35 kW/m^

^--typical ignition time scatter is on the order of ±10% (1 a) in most tests,

but high scatter is to be expected at irradiances near the minimum ignition

flux for a given material.

25
Table 2. White pine ignition times, showing effect of edge conditions

Orientation

Ignition time (s)

At irradiance (kW/m^

)

20 40 60 80

horizontal

no edge frame 25 ±4.9^ 4.7 ±0.4 3.7 ±1.0 1.9 ±0.3

with edge frame 58 ±6.3 5.1 ±0.2 4.0 ±1.0 3.0 ±1.4

vertical

with edge frame 285 ±150 16.4 ±2.2 6.3 ±0.9 3.5 ±0.9

^ ±1 a for three tests

26
Table 3. Effect of specimen conditions on ignition times for black PMMA

Ignition time (s)

Orientation Thickness Edge At irradiance (kW/m^

)

20 40 60

vertical 25 foil 208 ±8.9“ 42.6 ±1.4 19.6 ±1.9

horizontal 25 foil 180 ±6.4 42.5 ±4.7 18.6 ±1.1

horizontal 25 cardboard 40.5 ±4.1 19.3 ±0.3

horizontal 12 foil 42.8 ±8.9 21.5 ±0.3

® ±1 CT for three tests

27
Table 4. Comparative behavior of commercial flexible polyurethane foams

Irradiance (kW/m^

)

Specimen

A B C D

untreated untreated treated: Br treated: Cl, P (25 kg/m3) (21 kg/m3) (25 kg/m^) (28 kg/m^)

Ignition time (s)

25 5.5 5.2 39.2 15.0

50 3.3 3.3 4.1 4.1

75 1.3 N.A. 2.7 2.9

25 433

--Peak heat release rate (kW/m^)--

466 438 467

50 1059 876 1029 844

75 1773 1810 1429 1862

60 s. avg. heat release rate (kW/m2)

25 278 272 276 230

50 443 470 456 428

75 501 646 545 561

28
Table 5. Ignitability of air- supported fabrics

Specimen F/T F/Sa F/Sb F/Sc F/Sd PE/PVC

Fabric type fiberglass fiberglass fiberglass fiberglass fiberglass polyethyl

Surface coating PTFE silicone silicone silicone silicone PVC

Weight (kg/m^

)

1300 450 1130 1080 1230 950

Time to ignition

at irrad. =

35 kW/m^

(s)

N.I.^ N.I. 225 N.I. N.I. 17

75 kW/m^ 44 12 19 19 28 7

® --no ignition, for test exposure of 600 s

29
Table 6. Comparative ignitability results for red oak and black PMMA,

horizontal orientation

Ignition time (s)

Irradiance

(kW/m^

)

Red oak

(20 mm, with edge frame)

Black PMMA

(25 mm)

25 216 161

50 24.3 38

75 11.8 19.5

100 6.5 11.5

30
Table 7. Comparison of experimental PMMA results to simple predictive rules

Irradiance (kW/m^

)

lenition times ( s)

25 50 75 100

Measured in cone calorimeter 161 38 19.5 11.5

Measured by Hallman 145-158 35-37 15-18 8-10

Simple theory (Eq. 4) 140 20.8 8.0 4.2

Hallman's correlation (Eq. 6) 360 90 40 23

31
Table 8. Ignition times for Douglas fir particle board

Measured

Calculated ignition times (s)*

ignition

time

in

Based on m"=2 . 5 g/m^ Based on q"=30kW/m2 Based on T. =380“C i 8 Irradiance

(kW/m^

)

Cone

Calorimeter

(s)

w/o conv

.

cooling

with

conv. cooling

w/o

conv. cooling

with

conv. cooling

w/o conv

.

cooling

with

conv. cooling

25 100 143

(375 °C)

172

(372 °C)

168

(388 °C)

203

(385 *C)

153 189

50 25 30.4

(396 °C)

33.0

(395 °C)

36.5

(415 °C)

39.4

(413 °C)

25.7 28.2

75 12 13.6

(409 “C)

14.4

(409 “C)

16.4

(430 °C)

17.4

(429 “C)

10.2 10.9

100 8.5 7.7

(418 °C)

8.0

(417 °C)

9.4

(441 ’C)

9.8

(440 “C)

5.4 5.6

Surface temperatures at ignition are shown in parentheses.

32
Table 9. Effect of orientation on ignition times for aircraft panels

Ignition time (s)

Irradiance Orientation

(kW/m^

Specimen

Epoxy/

fiberglass

Phenolic/

fiberglass

Epoxy/

Kevlar

Phenolic/

Kevlar

Phenolic,

Graphite

25 horiz

31.6 27.9 33.0 N.I.^ N.I.

25 vert

29.8 N.I. 36.1 N.I. N.I.

50 horiz

7.8 8.0 8.8 8.0 12.2

50 vert

7.9 8.0 6.5 8.5 9.5

75 horiz

4.8 4.3 3.9 4.5 5.5

75 vert

5.8 5.5 5.5 5.5 5.5

^ N.I. = no ignition

33
Table 10. Ignition of building materials determined by four test methods

Specimen Thickness Weight Time to ignition (s) for 5 0 kW/m^ irrad

(mm) Cone

Calor

.

Hor.

Cone

Calor

.

Vert

ISO OSU STFI

insulating fiber 13 250 kg/m^ 1 5 12 5 10

board

medium density 12 600 kg/m^ 15 20 22 15 25

fiberboard

particle board 10 750 kg/m^ 15 25 30 20 25

gypsum plaster 13 700 kg/m^ 25 23 34 18 30

board

PVC wall covering 0.7 240 g/m^ 1 10 9 10 8 on gypsum board

paper wall covering 0.6 200 g/m^ 5 10 14 8 20 on gypsum board

textile wall covering 0.7 370 g/m^ 8 15 22 15 15 on gypsum board

textile wall covering 50 100 kg/m^ 10 12 13 5 12 on mineral wool

melamine faced 1.2 810 kg/m^ 100 145 26 _ _ a ^ ^ a particle board

polystyrene foam 50 20 kg/m^ 25 83 2 20 105

rigid polyurethane 30 30 kg/m^ 1 3 2 8 3 foam

wood panel, spruce 11 530 kg/m^ 10 15 18 10 15

paper wall covering 0.6 200 g/m^ 20 24 19 15 25 on particle board

-poorly defined time to ignition

34
Table 11. Effect of ignition time on peak heat release rate

Irradiance = 20 kW/m^

Ignition time® Peak q"

(s) (kW/m^

)

145 196

266 135

444 96

®--for 20 mm thick white pine speci

Irradiance = 40 kW/m^

Ignition time®

(s)

Peak q"

(kW/m^

)

13.9 220

17.4 241

18.0 223

, vertical orientation

35

•CJ'cNj
Figure 1. General View of Cone Calorimeter

36
37

Figure

2.

Detailed

View

of

Cone

Calorimeter

(vertical

orientation)
MEASURED

FLUX

(kW/m^)

Figure 3. Variations in Measured Flux for Actual Specimen

Face at Various Depths Below the Original Level

38
TIME

-

100x100mm

sample

(s)

Figure 4. Effect of Specimen Size on Time

to Ignition [8]

39
All dimensions in millimeters 2 5

2.5

r-rriTi 1 1 1 M 1 1 1 } 1

1

1 1 1 ; 1 III 1 III r ! 1

!' 1 1 ll~ ) —I

— k

1 t ~T~ 33

20 1 _L__jL_

SIDE VIEW

Figure 5. Holder for Fabrics for Air-supported Applications

40
S|

N0I1IN9I

01

3NI1

Figure 6. Ignitability Curves for Various Fabric/Foam

Assemblies

41
200

100

80

60

40

20

10

5

T

1 1 1 1—11 I I \

CONE CALORIMETER

\

\

_J I J I I I I IJ L_

20 40 60 80100 200

IRRADIANCE (kW/m2)

Figure 7. Results for Red Oak and Black PMMA

42
TIME

TO

IGNITION

(s)

Figure 8. Black PMMA Results Compared to

Hallman's Results

43
FO«M NBS-1 14A (REV.l 1-84)

U.S. DEPT. OF COMM. 1. PUBLICATION -OR 2. Performing Organ. Report No. 3. Publication Date BIBLIOGRAPHIC DATA

SHEET (See instructions)

REPORT NO.

NBSIR 86-3445 September 1986

4. TITLE AND SUBTITLE

IGNITABILITY MEASUREMENTS WITH THE CONE CALORIMETER

5. AUTHOR(S) Babrauskas and William J. Parker

6. PERFORMING ORGANIZATION (If joint or other than NBS, see in struction s) 7 . Contract/Grant No.

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

8. Type of Report & Period Covered

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

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

bibliography or literature survey, mention it here)

The Cone Calorimeter is a new- generation instrument developed primarily for

making rate of heat release measurements. This instrument, containing a uniform and well -characterized irradiance source, was also seen to be useful

for making measurements of radiant ignition on materials. Data have now been

collected for a wide range of materials. The effects of various apparatus

dependencies are discussed. Also, some comparative data are available illustrating the performance of similar materials in other apparatuses. Finally,

for a selected material, Douglas fir particle board, a detailed comparison with an ignition model has been made.

l<^£Y WORDS (Six f' entries; alphabetical order; capitalize only proper names; and separate key words by semicolon ij calorimeter; ignitability ; plastics; radiant ignition; upholstered

rurniture; wood materials.

13. AVAILABILITY

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I I For Official Distribution. Do Not Release to NTIS

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20402.

13^ Order From National Technical information Service (NTIS), Springfield, VA 22161

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15. Price

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