NBSIR 88-3733

MAY pv inoq

Research Information Center

‘National Bureau of .Standards

Gaithersburg, Maryland 2089S Cone Calorimeter Evaluation of

the Flammability of Composite

Materials

James E. Brown

Emil Braun

William H. Twilley

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

March 1988

Supported in part by:

U.S. Department of the Navy

Naval SEA Systems Command (NAVSEA 05R25)

Washington, DC 20362

Stimulating America s Progress 1913-1988

NBSIR 88-3733

CONE CALORIMETER EVALUATION OF

THE FLAMMABILITY OF COMPOSITE

MATERIALS

James E. Brown

Emil Braun

William H. Twilley

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

March 1988

Supported in part by:

U.S. Department of the Navy

Naval SEA Systems Command (NAVSEA 05R25)

Washington, DC 20362

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

TABLE OF CONTENTS

Page

List of Tables iv

List of Figures vi

Abstract 1

1. Introduction 2

2. Materials 4

3. Measurement Technique 5

4. Results and Discussion 6

4.1 Ignition 6 4.2 Rate of Heat Release 12

4.3 Fire Sensitivity Indices 19

4.4 Product Generation 22

5. Summary and Results

6. Conclusions and Recommendations

7 . Acknowledgments

8. References

24

26

26

27

iii
LIST OF TABLES

Page

Table 1. Composite Materials 29

Table 2. Ignition-Delay Times for Composite Materials

Exposed to Various External Flux Levels 30

Table 3. Ignition Temperature of Six Polymers as Measured by

by Thomason and Drysdale 31

Table 4. Surface Temperature of Coated and Uncoated Graphite

Fiber Reinforced Composites 3 mm Thick at Ignition 32

Table 5. Minimum External Flux for Long Exposure Time and for

300 Second 33

Table 6. Results of Averaging the Rate of Heat Release of

25 mm (1 in) Koppers Dion 6692T Panels (FR Polyester/

Fiber Glass Composite) 34

Table 7. Influence of Glass Fiber Configuration on the IgnitionDelay and Average Rate of Heat Release of Koppers Dion

Polyester Composite Irradiated at 50 kW/m2 35

Table 8. Interval Averaged Rate of Heat Release of 3 mm Corflex

Panels and a Panel Assembly (FR Epoxy-Fiber Glass

Composite) 36

Table 9. Interval Averaged Rate of Heat Release of 25 mm Thick Dow

Derakane Pump Housing (Vinyl Ester Epoxy-Fiber Glass

Composite) 37

Table 10. Interval Average Rate of Heat Release of 3 mm Thick

Laboratory Samples of Epoxy-Graphite Fiber Composite

Panels 38

Table 11, Results of Post- Ignition Averaging of the Rate of Heat

Release of 3 mm Thick Ryton Panels (Reinforced

Poly (phenylene sulfide)) 39

Table 12. Results of Post - Ignition of the Rate of Heat Release of

3 mm Thick Laboratory Samples of BMI Graphite Fiber

Composite 40

Table 13. Result of Pos t - Ignition Averaging of the Rate of Heat

Release of a 2-Ply Reinforced Vinyl Poly(styryl pyridine)

BMI Composite 41

Table 14. Comparison of Inferred Flammability Indices of Composite

Materials 42

IV
Table 15. Average Yields of Combustion Products for Various Types

of Composite Materials 43

Table 16. Ratio of Average Yields for C0/C02

, HC/C02 and C/C02 for

Various Types of Composite Materials at External

Irradiance 44

v
LIST OF FIGURES

Page

Figure 1. Schematic Representation of Cone Calorimeter 43

Figure 2. Range of Ignition Delay Times as a Function of External

Radiant Flux for All Composites 44

Figure 3. Ignition-Delay Time for Two Composites as a Function of

External Radiant Flux 45

Figure 4. Effect of Irradiance on the Rate of Heat Release from a 25 mm FR Polyester/Glass Composite 46

Figure 5. Effect of Irradiance on the Rate of Heat Release from a

3 mm FR Epoxy/Fiber Glass Composite 47

Figure 6. Effect of Irradiance of the Rate of Heat Release from

from 3 mm Poly (phenylene Sulfide)/Fiber Glass Composite 48

Figure 7. Effect of Irradiance on the Mass Loss Rate from a FR Polyester/

Fiber Glass Composite 49

Figure 8. Effect of Irradiance on the Mass Loss Rate from a 3 mm Thick

FR Epoxy/Fiber Glass Composite 50

Figure 9. Effect of Irradiance on the Mass Loss Rate from a 3 mm Thick

Poly (phenylene Sulf ide ) /Fiber Glass Composite 51

Figure 10. Average q as a Function Time After Ignition of Irradiatively

Heated Koppers Dion 6692T Composite (FR Polyester/Glass)

Panels 52

Figure 11. Average q as a Function of Time After Ignition of

Irradiativel Heated 3 mm Corflex (FR Epoxy/Glass)

Panels 53

Figure 12. Average q as Function of Time After Ignition for

Irradiatively Heated 3 mm Ryton Panels ( Poly (phenylene

sulf ide)/Fiber Glass) 54

Figure 13. Average Rate of Heat Release Up to 60 s Post Ignition of

Several Composites as a Function of External Flux 55

Figure 14. The Effect of Irradiance on the Production of C02 from 25 mm

FR Polyester-Fiber Glass Composite 56

Figure 15. The Effect of Irradiance on the Production of CO from a FR Polyester/Fiber Glass Composite 57

vi
Cone Calorimeter Evaluation of

the Flammability of Composite Materials

By

James E. Brown

Emil Braun

William H. Twilley

Abstract

A study was undertaken to evaluate the fire performance of composite materials

using the cone calorimeter as the bench-scale method of test simulating the

thermal irradiance from fires of various magnitudes. Five parameters were

derived from the calorimetry measurements to characterize the ignitability and

flammability of the composite materials.

Three of the parameters are, to a large extent, empirical since radiative heat

losses from the samples were unknown-. These parameters are: 1) minimum

external radiant flux (MERF) required to produce pilot ignition in a

predetermined exposure time; 2) thermal sensitivity index (TSI) which

indicates the burning intensity dependence on external heat flux; and 3)

extinction sensitivity index (ESI) which indicates the propensity for

continued flaming combustion without an external heat flux. MERF values at

300 s for 3 mm composites panels of a FR epoxy resin and a poly (phenylene

sulfide) (PPS) resin composites were about 18 and 28 kW/m2

, respectively. The

TSI of the PPS resin composite had the greatest dependency on external flux.

Additionally, the ESI of the PPS composites was the only one to indicate an

external flux requirement to sustain combustion during the first 60 s after

ignition. The other two parameters determined were yields of gaseous products

of combustion and average extinction area, a, normalized to the C0 9 yields.

1
The values were found to be essentially constant at external fluxes ranging

from 35 to 75 kW/m2

, with few exceptions

1. Introduction

The purpose of this project is to assist the Navy with selection criteria for

ship components made of synthetic resins or composites of fiber-reinforced

resins by systematically assembling data on the flammability properties of

these materials. The ultimate use of such a data base assembly is input for a

method for accurately predicting the real fire performance and flammability

characteristics of composites and resins from bench-scale tests. This is an

interim report.

There are numerous naval ship components where the use of composites would

provide substantial advantages over metals with respect to weight reduction,

corrosion resistance, and design simplification. Furthermore, for some

applications, the non-magnetic character of composites is uniquely

advantageous. On the other hand, the resin matrix of a composite, being an

organic component, presents an increased potential for fire hazard. Hence, in

order to make wise engineering decisions assessing trade-offs, such as weight

savings versus flammability, information must be available on the fire

performance of candidate materials in various fire scenarios. A recent review

[ 1

]

found no report of bench- scale test methods by which the fire performance

of materials could be predicted.

Number in brackets refer to references given at the end of this report.

2
The primary objective of this phase of the study is to determine the rate of

heat release (RHR) of selected composites and resins burned under various

levels of radiative heating. These levels simulate fire scenarios in which

the composite material is itself burning or in which it may be near another

burning material. The rate of heat release, q, of fires, especially the peak

q, is the primary characteristic determining the size, growth, and suppression

requirement of a fire environment [2]. This flammability characteristic can be

measured using a bench-scale instrument. These values approximate the RHR of

a surface element of a full-scale object in a real fire environment. Combined

with other measurements, such as flame spread rate (the rate of growth of the

surface element) and ease of ignition, the fire hazard contribution of the

object can then in principle be calculated. Some such computational methods

are already under development for other applications [3].

The calculations of Huggett [2] demonstrated that the average heat of

combustion for a broad range of materials is a constant 13.1 kJ/g oxygen

consumed, with an accuracy of ± 5% or better. Thus the RHR can be determined

with good accuracy from two simple measurements, the flow rate of air through

the combustion system and the oxygen depletion in this flow [4], A benchscale apparatus, the Cone Calorimeter, developed and described by Babrauskas

[5], utilizes this oxygen consumption principle to determine the RHR per unit

area q" . The name "Cone Calorimeter" was adopted from the geometric

configuration of its radiant heater. Data from this instrument can be used in

research to predict the full-scale fire behavior of certain furnishings and

wall lining materials [6], The predictive method defines an environment as

3
having n objects with surface areas divided conceptually into m small uniform

areas, A, during combustion, so that q at any time is given by

’ a)

The Cone Calorimeter has a well characterized and controlled irradiance

source. Babrauskas and Parker [7] deduced that the spectral distribution of

this source approximates the irradiance in compartment fires, where radiation

is the primary process for energy transfer. Thus it was concluded that the

instrument suitably determines the ignitability of upholstery and wood in

fire- like environments.

We report the results of Cone Calorimetry measurements on a variety of

composites and materials typical of those which may be used in ship

components. The primary measurement using the Cone Calorimeter is RHR as a

function of time under pre-selected, constant levels of irradiance simulating

radiant fluxes from real fires of various magnitudes. Simultaneouslydetermined time - to - ignition , mass loss, combustion product yields, and smoke

obscuration are also reported.

2.0 Materials

The materials used in this study are listed in Table 1. For the most part,

only the generic classification of the resin and a general classification of

the fiber reinforcement are known. Where greater detail of the materials is

available, it will be indicated when the test results are presented. The

generic classification of the resin and fiber identification were provided by

the indicated sources. In general, the resin reinforcement was a glass fiber

4
ton* fabric except for a sample set of Ry * * panels in which carbon fibers were

used. Several tests were performed on composite materials for which neither

the identity of the fiber nor the resin was known. These latter tests were

performed at the specific request of the Navy.

Test specimens were cut into 10 cm by 10 cm squares at the full thickness of

the supplied product. The specimens were maintained at laboratory conditions

(approximately 40-45% RH and 25°C) prior to testing.

3.0 Measurement Technique

The data reported here were obtained using the NBS Cone Calorimeter which is

shown schematically in figure 1. The Cone Calorimeter and its function have

been previously described by Babrauskas [5] and Babrauskas and Parker [7],

Briefly, it is a bench-scale rate of heat release calorimeter based on the

principle of oxygen consumption [2]. The energy release rate is computed from

the measurements of mass flow rate and oxygen depletion in the gas flow

through the exhaust stack. An external radiant energy flux of up to 110 kW/m2

may be applied to the surface of a sample by a temperature-controlled radiant

cone heater. An electric spark igniter mounted above the specimen was used to

ignite the pyrolysis products generated by a specimen exposed to a preset

irradiance. The ignition delay time for each composite material usually was

* Certain commercial materials are identified in this report in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation by the National Bureau of Standards nor

does it imply that the material identified is necessarily the best available

for the purpose.

5
measured at three different radiant flux levels. In general, specimens are

exposed to flux levels of 35, 50, and 75 kW/m2

. Ignition delay time

measurements were made by an operator with a stop watch as part of the

standard test procedure used to determine the rate of heat release. Samples

were placed under the cone heater and the amount of time necessary to ignite

the evolving decomposition products by the spark of an electric arc was

recorded.

A load cell was used to continuously measure changes in sample mass, while

products of decomposition, (i.e., CO, C02

, and total unburned hydrocarbons)

were monitored by appropriate gas analyzers. By combining the mass loss data

and the gas concentration data, specific gas species yields were computed

(mass of product/unit mass of material gasified) . Smoke obscuration was

characterized by the attenuation of a laser beam and reported as the

extinction area per unit mass of material consumed. Data from all the

measurement devices were collected every five seconds by a digital data

acquisition system and stored for later data reduction.

4.0 Results and Discussion

4 . 1 Ignition

The objective here is to obtain a measure of the resistance of materials to

pilot ignition under radiative heating. The number of different radiant flux

levels and the replication number were limited by material availability.

6
Therefore, for example, the Koppers Dion sample was tested in duplicate at

four flux levels (the three cited above plus 25 kW/m2

) , while ignition of the

Corflex assembly was measured at only three flux levels.

The times to pilot ignition are reported in Table 2. Where duplicate

measurements were made, the average values are reported (one half of the

difference between the two measurements is shown in parentheses) . As

expected, the data show that as the incident flux increases the ignition delay

time decreases. It should also be noted that the range of ignition delay time

for all materials tested at a given radiant flux increased with decreasing

radiant flux (figure 2) , with ranges of 21 s to 55 s at 75 kW/m2 and 92 s to

390 s at 35 kW/m2. Therefore, in very large fires, one might expect similar

ignition- delay times for all composites, whereas in incipient fires one would

expect ignition-delay times to depend on the chemical composition of the resin

and configuration of the material.

There are two possible modes of radiative ignition: one is auto - ignition and

the other is pilot ignition. Auto- ignition results solely from the external

heating of the material substrate, without the presence of a high temperature

source near the material surface. Pilot ignition refers to forced ignition of

the fuel vapors by a high temperature pilot source such as a hot wire, spark,

or small flame. For auto - ignition to occur, the fuel/air ratio above the

material substrate must be within the flammability limits and the gas phase

temperature must be above an ignition temperature. Because of the existence

of an intentionally supplied hot spot, pilot ignition only requires that the

7
fuel/air ratio above the material substrate in the vicinity of the pilot

source be within the flammability limit.

The gasification (pyrolysis) rate of the resin controls the speed at which the

vapor concentration at the composite surface approaches its lower flammability

limit. The gasification rate is temperature dependent. Therefore, it appears

reasonable to suppose that ignition occurs only after the surface temperature

of the resin has reached a critical level, the ignition temperature. This

ignition temperature could vary somewhat with ignition conditions, such as

heat flux level, on char- forming materials due to the insulating effect of the

char

Kashiwagi [8,9] investigated the effect of external radiant flux on the

surface temperature at ignition and the ignition delay time of red oak and

poly (methyl methacrylate) (PMMA) in auto- and pilot- ignition modes. He used a

high powered C02 laser to irradiate (60-160 kW/m2

) the sample surface, while

simultaneously measuring sample surface temperature with a small diameter

chromel -alumel thermocouple. An electrically heated wire was placed near the

sample surface for pilot - ignition tests. These tests showed

that for PMMA the surface temperature of the substrate at ignition was

relatively constant, approximately 400°C, for both auto- and pilot- ignition

modes. The surface temperature of red oak, a char former, at ignition

increased as the external flux decreased.

Atreya [10] reported results of tests on different types of wood and found

that, for the pilot- ignition mode below an external flux of 25 kW/nr , the wood

8
surface temperature at ignition increased with decreasing external radiant

flux. Above 25 kW/m2 the surface temperature at ignition was constant at

approximately 350°C.

Rasbash et al. [11] used an electrically heated radiant panel to irradiate

samples of PMMA at 11 kW/m2 and above. Using a small hydrogen flame as a

pilot, they found that surface temperatures decreased slightly with decreasing

external radiant flux. At 24 kW/m2

, the reported surface temperature was

about 275°C and decreased to 250°C at 11 kW/m2

. This is about 150°C below the

value reported by Kashiwagi [9]. Instrument-dependent conditions for surface

temperature measurement may account for the differences in pilot- ignition

results between Kashiwagi and Rasbash.

Thomson and Drysdale [12] measured the surface temperature at ignition in the

presence of a pilot flame of six common thermoplastics using two different

instruments over an irradiance range of 10 kW/m2 to 40 kW/m2

. Table 3

summarizes their results. Within experimental error, they found that the

surface temperature at ignition was not significantly affected by changes in

the level of external radiant flux, above some minimum value. This is

indicative of a unique ignition temperature for a range of irradiance levels.

These thermoplastic materials are known to undergo gasification by pyrolysis

without significant secondary reactions such as char formation reactions.

Simple bond scission of aliphatic carbon chains will lead to volatile and

combustible products.

9
Brown [13] recorded the surface temperature of a series of composite panels

exposed to different radiant flux levels in the cone calorimeter. Table 4

summarizes those results for the surface temperature at pilot ignition using

an electric spark. While the data show some scatter, in general, the surface

temperature at ignition is relatively constant for each material and is

greater than the thermoplastics above (Table 3) due to enhanced stability from

cross links and aromatic components.

All of the materials listed in Tables 3 and 4 behave qualitatively the same as

those shown in figure 2 with respect to ignition and radiant flux. The

presence of inorganic fibers does not appear to alter the ignition behavior.

If it is then assumed that this trend is applicable in general to all

composites (i.e. that the pilot ignition occurs at a fixed surface

temperature, dependent only on the thermal gasification characteristics of the

substrate) , one can use the simple thermal heat-up model’ derived by Carslaw

and Jaeger [14] to suggest a form or trial function that ignition-delay time

might have with respect to the heat absorbed from the constant external

radiant flux. Heat losses are ignored in this simple model. Furthermore,

this model assumes that the substrate can be treated as an inert, thermally

thick, and opaque solid. Then the delay time to reach the ignition

temperature is given by:

c is (2)

where

t ig = ignition delay time (s)

k = thermal conductivity (kW/m/K)

p = density kg/m3

)

10
c = heat capacity (kJ/kg/K)

Tig = ignition temperature (K)

TQ = initial temperature (K)

q = external radiant flux absorbed at the surface of the solid (kW/m2

)

Equation (2) shows that the ignition delay time, t A , is proportional to 1/q2

provided, however, that the temperature wave does not reach the back surface

of the sample before ignition. If, however, the material is thermally thin,

that is, if the thermal wave hits the back surface before ignition occurs, the

solid material will have an ignition delay proportional to about 1/q.

Additionally, equation 2 provides an approximate basis for determining the

influence of k, p, and c on ignition behavior. Therefore, a log- log plot of

ignition time versus flux should give a straight line with a slope of minus 2

for an inert, thermally thick, and opaque material. Figure 3 shows the

results for the Koppers Dion 6692T panel 25 mm thick and a Corflex panel, 3 mm

thick. A linear regression line drawn through these data results in negative

slopes for the two lines of 2.3 and 1.7, respectively, for the Koppers and

Corflex panels. Table 5 is a listing of the slope of the regression line for

each composite. It is recognized that derived values are essentially

empirically based since heat losses are not known. However, plots of the data

appear to be linear as was shown by typical examples in figure 5. Moreover,

ignition apparently occurs before the thermal wave penetrates the back

surface

Plotting ignition-delay data for all Cone Calorimeter experiments (Table 2) as

illustrated in figure 3 allows one to extrapolate the regression line to some

chosen location. Extrapolation to 600 s, the recommended time limit for

ignition in this apparatus, represents the minimum external flux (MERF)

11
necessary to produce pilot ignition after a protracted exposure of 600 s to

irradiative heating. The MERF values (at 600 s) are listed in table 5,

although these values may not be completely realistic because of the extensive

extrapolation (for some materials) from a limited data range. Moreover, a

real fire on a ship, whose radiant flux requires at least 600 s for pilot

ignition of a composite material, is expected to be detected and suppressed

before the composite becomes involved in the fire growth. A more practical

application of the ignition times would involve determining the required

irradiance to cause ignition at some other time, such as 300 s, for example.

This represents an estimate of the maximum external flux from a fire in the

environment where composites are used that the composite could withstand

before the material would begin to contribute to the fire growth. The values

obtained at 300 s are also listed in Table 5 and are called MERF3 0. Although

the data for ignition are very limited, the maximum deviation of the

regression slope from the theoretical value of minus 2 towards a value of

minus 1, was 0.5 (25%) for the 3 mm Derakane panel. This difference, in part,

may be due to heat loss from the back surface of the thin sample. Similar

effects may be attributed to the thin Corflex panel even though the regression

slope, minus 1.9, closely approximates the idealized value, minus 2. These

materials indicate the lowest MERF values for ignition 12 and 18 kW/m2

,

respectively, for MERFg 0

and MERF3 0

.

4.2 Rate of Heat Release

We present in this section the Cone Calorimeter results on the heat released

as measured by the oxygen consumption during the combustion of several

12
materials under radiative heating in a fully ventilated atmosphere (21%

oxygen). It has been established [2] that the carbon in organic materials

need not be fully oxidized to carbon dioxide for the relationship of 13.1 kJ

of heat released per gram of oxygen consumed to hold true. Thus, typical

reaction products of combustion in fire environments, consisting of partially

oxidized pyrolysis products, such as, hydroxy and carbonyl compounds and soot,

do not significantly affect the accuracy of the Cone Calorimeter results.

Results of heat release rates were obtained here for a broad range of resins,

including epoxy, polyester and poly(aryl thio-ether) resins, whose structures

and chemical compositions are very different, suggesting individual degrees of

susceptibility to oxidation and gasification under radiative heating.

Profiles of the rates of heat release with respect to time, under constant

external irradiance , were found to have features which are unique to the

composite studied. The profiles appear to depend primarily on the chemical

composition of the resin and the thickness of the composites. Figures 4, 5,

and 6 demonstrate typical variations observed in the RHR- time profiles of,

respectively, a 25 mm (1 inch) thick polyester/glass fiber (Koppers Dion

6692T) , a 3 mm (1/8 inch) thick epoxy/glass fiber panel (Corflex) , and a 3 mm

thick poly (phenylene sulf ide)/glass fiber (Ryton) composite panel, each of

which was radiatively heated at 35, 50, and 75 kW/m2

. The polyester composite

also was radiated at 25 kW/m2

. In each of the figures, the curves for the

composite generally show an initial sharp rise in the RHR which occurs at

about the time of ignition and increases to a maximum or peak RHR for each

irradiance level. The peak RHR duration is short. The subsequent decrease in

13
irradiance level. The peak RHR duration is short. The subsequent decrease in

initial RHR is attributed to increase in thickness of the char layer. The

char layer reduces the transfer of heat to the substrate (resin) below the

surface thereby reducing the rate of gasification of the resin.

In general, all of the curves exhibit at least two maxima for RHR. The

initial peak is due to surface volatilization and char formation, as discussed

above. The second peak is a result of an increase in the gasification rate of

the unburned substrate (mass loss rate data will be discussed below) caused by

an increase in the bulk temperature of the substrate. The bulk temperature

increases because the unburned substrate is no longer thermally thick, i.e.,

the thermal wave has reached the back surface. Back surface temperatures

should increase as the second peak of RHR is approached. While these

measurements were not made in this investigation, Parker [15] has shown the

same phenomenon with wood, a char forming material. He observed two maxima in

RHR; the second peak increased as the back surface temperature increased.

The separation with respect to time of the RHR maxima is dependent on the

sample thickness, irradiance level and chemical composition of resin. For

example, the 3 mm thick Corflex and Ryton panels tested at 35 kW/m2 have peak

o separation times of about 150 s and 350 s, respectively. This difference is

attributed to the chemical composition of the resins, the difference in

thermal properties, and difference in flame heat feedback rates.

It may be seen that the intensity of the RHR follows the r^ce at which

volatiles are pyrolyzed from the specimens, and, to a large extent, is

14
indicative of the thermal stability of the resin and its propensity to gasify.

The mass loss rates with respect to time of the polyester, epoxy, and PPS

composites are shown, respectively, in figures 7, 8, and 9. The purpose of

presenting the mass loss curves at this time is to show that the dq"/dt versus

time curves follow the time profile of mass loss rate, dm"/dt, versus time

curves. The ratio of these two quantities (q"/in") at any given time is the

effective heat of combustion (Ahc eff ) of the gases evolved at that time. The

mass loss rates and heat of combustion will be discussed further in a later

section

Since the RHR, in most cases, changes quite significantly with time, it

appears that more meaningful information may be gained about the fire behavior

of the composites under radiative heating if the rates of heat release are

averaged over periods of time during the burning process . Not only are the

advantages of curve smoothing brought forward to clarify trends in the heat

release data, but Babrauskas and Krasny [16] demonstrated that the rate of

heat release averaged over 180 s could best be used to predict the fire

performance of upholstered furnishings in large-scale experiments. Kanury

and Martin [17] also have used average values for deducing physicochemical

properties of essentially homogeneous materials in fire environments. The

proposed ASTM Method P 190 [18] specifies that average q" values for the first

60, 180, and 300 s after ignition, or for other appropriate periods, be

included in the report of the cone calorimeter results. In addition to the

recommended practice in ASTM P 190, the average RHR over 60 s intervals from

ignition are reported.

15
Figure 10a shows a plot of the RHR averaged as recommended in P 190 from

ignition up to 360 seconds for the Koppers composite under the four irradiance

levels previously mentioned. A similar plot, figure 10b, shows the 60 s

interval averages for the RHR. As expected, the recommended procedure shows a

rather smooth change in the average RHR up to 360 s after ignition. In every

case this includes the initial peak RHR's but may not include the second

maximum. The effect of irregular volatilization of fuel from the surface is

reduced. Figure lib shows a more irregular pattern. However, the first 60 s

intervals are identical. Figures lla/llb are similar plots for the Corflex

composite which shows more distinction between the irradiance levels for the

first two minutes. Thereafter, the curves tend to coalesce or merge around

180 seconds after ignition as the effect of the back surface is felt.

Figures 12a/12b demonstrate the behavior of the average RHR of Ryton composite

over the post- ignition period. This composite shows, as previously suggested,

the greatest sensitivity to irradiance level. The lowest irradiance level, 35

kW/m2

, as was seen in the ignition data, provides barely enough energy to

promote combustion. On the other hand, the average RHR at irradiances of 50

and 75 kW/m2 provides for an increasing average until 300 and 240 s,

respectively, when the panels are burned out.

The cone calorimeter results obtained in this study on the rates of heat

release averaged at the various times, as previously indicated, are presented

in tables 6 through 13 . Table 6 presents all of the results obtained for the

25 mm thick Koppers polyester composite. This table includes the data

illustrated in figure 10. The q" value averaged at 60 s for one of the

16
specimens tested at 35 kW/m2 appears to be larger than expected. An

explanation for this behavior is not known at this time.

Table 7 summarizes average RHR, q"(t), values for a 13 mm (1/2 in) thick

Koppers polyester composite consisting of various configurations of glass

fiber reinforcements in composites containing 42% and 54% of brominated (fire

retardant) polyester resin and in composites containing 42, 43, and 51% of the

non-brominated polyester matrices. The glass fiber reinforcements in the

composites include (1) fibers woven into a mat from continuous strands and

then stitched along with other chopped fibers (stitched woven roving and

chopped strand); (2) reinforcements from woven roving and woven mat; and (3)

non-woven spirally interlocked fiber mat. The effect of bromine as a flame

retardant can be seen readily by comparing the average q" values at 60 s of

the untreated samples (first three samples listed) with the two bromine

containing samples. It appears that the presence of bromine in the polyester

results in a reduction of average q"'on the order of 35 to 40% overall. On

the other hand, we note that the average q" values of the brominated specimens

in this table (which were 13 mm thick) are generally a factor of two greater

than the average q" of the 25 mm specimens radiatively heated at 50 kW/m2

shown in table 6. The difference in any rate of heat release may be

e attributed, in part, to the difference in sample thicknesses, i.e., 25 mm

versus 13 mm, but other unknown factors are also responsible for the early

differences. The thicker samples provide a greater heat sink resulting in a

smaller volume of resin being raised to the decomposition temperature per area

of surface irradiated. This trend is also seen in T at about 40 s for the i g

13 mm sample and T i of about 60 s for the 25 mm sample (Table 2).

17
Next, the average q" values are summarized for three types of epoxy resin

composites. The average q" values of a fire retardant epoxy are listed in

Table 8. Tests were performed on the assembly as received and on the

individual outer panels. These results show that there are only small

differences between the average RHR values of the thermally thin (3 mm) and

thick assemblies (about 37 mm) and suggest that the heat loss from the back

surfaces of the thin samples is relatively small as a result of effective

insulation in the sample holder. The results for the composite with a vinyl

ester type of epoxy resin are listed in Table 9. The average q" results for

the third resin type, high performance epoxy resin composite prepared at DTRC

laboratory [13], are shown in Table 10. Although the composition of the resin

is not known beyond it being an amine-cured epoxy resin, it appears that the

fire performance of this latter resin closely resembles that of the FR epoxy

composite shown in Table 8.

Table 11 summarizes the average RHR of the four Ryton (PPS) panels. We note

that ignition did not occur when specimens reinforced with woven carbon fibers

were heated at a flux of 35 kW/m2

. The same result was found for one specimen

reinforced by a swirl mat of glass fibers. Overall, the RHR at this flux

level is low. Where results< are not reported at the various post- ignition

times, sustained flaming combustion did not occur. The average q" results of

another composite prepared at DTRC from a bismaleimide (BMI) and graphite

fibers and tested at NBS are listed in Table 12 [13]. The results from an

experimental composite, prepared from vinyl styryl pyridine and BMI, and

reinforced with glass fibers are shown in Table 13. This experimental

18
composite which is designed as a heat shield, is composed of only two plies of

fibers (- 1 mm) . Having such a low mass per unit surface area contributes to

low rates of heat release and fairly short periods of flaming combustion.

It may be seen in reviewing the average q" data in Tables 6 through 13 that

the composites with polyester and epoxy resins generally show maximum q"(t)

values in the first 60 s post ignition. The q"(t) values generally decrease

with time after the first 60 s which suggest that the peak RHR is associated

with initial surface burning of the composite rather than subsequent

combustion of the pyrolyzate from the interior of the composite. For

irradiances of 50 kW/m2 or more, the composites with PPS , BMI , and vinyl

poly(styryl pyridine)BMI resins show maxima at times greater than 60 s. For

these samples, the maximum q"(t) is not the initial peak.

4.3 Fire Sensitivity Indices

Kanury and Martin [17] and Kanury [19] reported simplified models by which

heat release rates (peak, instantaneous, and average values) may be related to

basic properties of materials in fire environments using the Spalding B number

concept. These authors and Tewarson and Pion [19] deduced from energy

conservation at the sample surface that the heat release rate q" may be

expressed by the following equation

9" = (AHc , e££ /L)[q[' + q" - q? ] (3)

where

19
L

It

4;

effective heat of combustion

heat of gasification (pyrolysis)

heat transferred from flame to material surface

imposed external flux

heat flux loss by the surface to ambient

The slope (AHc ff /L) of a plot of the measured RHR against the external

radiant flux

p rovides one measure of the flammability of materials; it is a

key determinant of the B number value. This parameter, the thermal

sensitivity index (TSI) [17], provides a basis by which the fire performance

of the materials may be indexed and compared over a broad range of external

irradiances, simulating different fire environments. The intercept of such a

plot in principle indicates whether the flame is self-sustaining in the

absence of an external irradiant flux for the time period under consideration.

We will call this parameter the extinction sensitivity index (ESI); Kanury and

Martin [17] called this parameter the limiting thermal index. Equation 3 can

be expressed as

q" = (TSI )

•

q

e + (ESI). (4)

We illustrate the dependence that the average RHR has with respect to imposed

heat flux levels by plotting the average q" at 60 s versus external flux,

q£ . Using 60 s average q" minimizes the effect of sample thickness and

conductive heat losses. Figure 13 show the results for composites whose

resins are polyester, FR epoxy, poly (phenylene sulfide), and BMI . This plot

illustrates the TSI and ESI at 60 s interval on resin composition.

20
Table 14 summarizes the slopes, intercept, average effective heat of

combustion, and minimum external radiant flux (MERF300 ) necessary for ignition

within 300 s. The ESI values (slopes) are estimates of the sensitivity of the

combustion intensity to variations in external irradiance and show that the

Koppers composite, Corflex Panel Assembly, and BMI Panel had about the

same sensitivity to variations in q-". Because of differences in sample

thickness these samples should not be compared to each other without caution.

However, the TSI values indicate that the rate of heat release of these

samples, although not the same in magnitude, would be fairly insensitive to

small changes in external irradiance. This suggests that in a real fire the

decay in an external fire imposing energy on a target material made from one

of these composites would not be reflected as rapidly in a reduced heat

release rate of the target material as compared to the materials with higher

TSI values. For example, the Ryton Panels, which ranged in value from 1.3 to

1.8, would be expected to respond most strongly to variations in source

irradiance

The Ryton Panels also exhibited a negative intercept, ESI. This suggests that

the heat loss from the flame is greater than its flux to the surface. With

the removal of an external heat source these materials can be expected to

self -extinguish , while the other materials with a positive ESI would be

expected to continue burning at least for the first 60 s. The intercepts

indicate that the epoxy matrix composites exhibit the most potential for

sustained combustion with an external radiant flux following ignition.

21
In Table 14, the effective heat of combustion values are averages taken

from each exposure over the entire measurement; they are computed from the

ratio of q" to mass loss rate, m

1 ' . These values fall into two groups, the

lower one (about 12 kJ/g) where the resin is flame retarded and the upper

values (20-25 kJ/g) where it is unretarded.

The minimum external radiant flux (MERF3 Q 0

) values necessary for ignition

within 300 s are repeated here for comparative purposes; ignitability is

another important flammability parameter that does not depend on the same fuel

characteristics as rate of heat release.

4.4 Product Generation

Table 15 summarizes the combustion product yields and mass loss at the various

radiant flux levels. Average values obtained from entire experimental periods

are reported since the quantities generated remained fairly constant with time

(see figures 18 and 19 for CO and C02

, respectively). The values for

hydrocarbons (HC) , CO, and C02 yields have been normalized to the sample

weight loss. While all of these tests were conducted under well -ventilated

conditions, combustion efficiency can still be determined by the C0/C02 ratio

and the HC/C02 ratio, Table 16. The data indicates that, in general, the

C0/C02 ratio is independent of external irradiance , with the exception of

Ryton Swirl Mat Panel. For this panel the C0/C02 ratio decreases with

increasing irradiance. The Koppers composites show a flux dependence on the

HC/C02 ratio such that it decreases with increasing flux, while the other

materials are constant with flux variations.

22
Smoke obscuration reported here is the average specific extinction area

cr(avg) , given by

a(avg) = [(2i Vi At)/(mi -mf )] [ ( 1/L) in(

o /I )

]

(5)

where

V flow rate in exhaust duct (m3 /s)

time interval of measurement (s)

mass loss (kg)

distance through which light is measured (m)

initial light intensity

final light intensity

In Table 16 are listed the a/C02 ratios for the materials tabulated in Table

15. In general, the a/ C02 ratio is constant for a material over the range of

irradiances investigated. However, as with the HC/C02 ratio, the a/C02 ratio

for the Koppers composite show a similar apparent dependence on external

irradiance. Also the a/C02 ratio for the lab epoxy, BMI , and Ryton Swirl Mat

are an order of magnitude less than the Corflex Panel and nearly two orders of

magnitude less than Koppers. This indicates that one of these three materials

would be best suited for applications where smoke obscuration is a primary

concern.

23
5.0 Summary of Results

The cone calorimeter was used to evaluate the fire characteristics of a series

of composite materials. Ignition delay time, heat release rate, yield of

gaseous products and smoke were measured.

The results of an analysis of the ignition delay time data showed that:

• T ig a 1/q2 was a usable, but simplified approximation of the data;

one must be cautious in extrapolating the data with it.

• This relationship applied to all of the composite materials

including the sandwich assembly (i.e. Corflex)

• There is some indication that the slope of the regression line,

for a given material composition is a function of the thickness of

the material (e.g. Derakane Panels and Corflex Assembly versus

Corflex Panel) .'

.

• Given the limited data set, glass fiber configuration appear to

have no effect on ignition delay time.

The results of an analysis of heat release rate data show that:
• Thermal sensitivity index (TSI) and extinction sensitivity index

(ESI) can be inferred from the external heat flux dependence of

the average rate of heat release during the first 60 s after

ignition.

• The TSI and ESI values were inferred from averaged RHR data

related to the external flux by regression analysis as defined to

show

q" = TSI-q" + ESI

• TSI values indicate a dependence of fire growth rate on external

flux during combustion.

• ESI values indicate whether a composite is expected to selfextinguish during the first 60 s of combustion if the external

heat flux is removed.

• Comparison of the TSI or the ESI values to MERF values show no

correlation

Product generation data show that the HC/C02

, C0/C02, and ct/C 02 ratios were

essentially constant with external irradiance (from 35 kW/m2 to 75 kW/m2

) for

the various composites tested. However, three exceptions were found:

• a FR polyester and a FR epoxy resin composites showed a decreasing

HC/C02 ratio with increasing external, irradiance;

25
• the PPS composite showed a decrease in C0/C02 ratio with

increasing external irradiance; and

« the PPS and BMI resin composites a/C02 values were an order of

magnitude less than the epoxy and polyester resin composites.

6.0 Conclusions and Recommendations

The Cone Calorimeter can measure an array of flammability parameters for

composite materials. These include the external radiant flux requirements for

pilot ignition and sustained flaming combustion, the flux dependency of the

rate of heat release, and the relationship of flux level to combustion

efficiency as reflected in the yields of combustion and pyrolysis products.

Since these measurements are based in the fundamentals of fire science, we

expect they will correlate well with the larger-scale compartment fire

behavior

Thus, this development represents the first step towards predicting the

performance of composite materials in various fire environments. Therefore,

we recommend investigating the use of these parameters from the Cone

Calorimeter and, additionally, a radiant- flux-based flame spread index to

provide the basic data from bench-scale measurements for correlation with

larger-scale (quarter scale and full scale, for example) compartment fire

measurements. The bench-scale parameters will then serve as input for hazard

prediction models of the type already under development at the NBS Center for

Fire Research.

26
Acknowledgments

This work was supported in part by the U.S. Department of the Navy, Naval Sea

Systems Command, (SEA 05R25) , Washington, D.C. The authors are grateful for

the cooperation of Mr. George Wilhelmi, Mr. Usman Sorathia, and Mr. James

Morris of DTRC , Annapolis, MD in obtaining and providing test materials.

27
References

[1] Brown, J.E,, Loftus, J.J., and Dipert, R.A. , "Fire Characteristics of

Composite Materials: A Review of the Literature", NBSIR 85-3226, U,S.

Dept, of Commerce, National Bureau of Standards, Gaithersburg, MD 20899.

[2] Huggett, C., "Estimation of Rate of Heat Release by Means of Oxygen

Consumption Measurements", Fire and Materials, 4, 61 (1980).

[3] Bukowski , R.W. , Jones, W.W. , Levin, B.M. Forney, C.L., Stiefel, S.W.,

Babrauskas , V., Braun, E., and Fowell, A.J., "Hazard I. Volume 1: Fire

Hazard Assessment Method", NBSIR 87-3602, U.S. Dept, of Commerce,

National Bureau of Standards (1987)

[4] Parker, W.J., "Calculation of Heat Release by Oxygen Consumption for

Various Applications", J. Fire Sci. 2, 380 (1984).

[5] Babrauskas, V., "Development of the Cone Calorimeter - A Bench- Scale

Heat Release Apparatus Based on Oxygen Consumption", Ibid 8, 81 (1984).

[6] Babrauskas, V., "Bench-Scale Methods for Prediction of Full-Scale Fire

Behavior of Furnishings and Wall Linings", Technology Report 84-10,

Society of Fire Protection Engineers, Boston, MA.

[7] Babrauskas, V. and Parker, W.J., " Ignitability Measurements with the

Cone Calorimeter", NBSIR 86-3445, U.S. Dept, of Commerce, National

Bureau of Standards (1986).

[8] Kashiwagi, T., "Experimental Observation of Radiative Ignition

Mechanisms", Combustion and Flame, 34, 231-244 (1979).

[9] Kashiwagi, T., "Effects of Sample Orientation on Radiative Ignition",

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

[10] Atreya, A., "Pyrolysis, Ignition and Fire Spread on Horizontal Surfaces

of Wood", NBS -GCR- 83 -449 , U.S. Dept of Commerce, National Bureau of

Standards (1984).

[11] Rasbash, D.J., Drysdale , D.D., and Deepak, D., "Critical Heat and Mass

Transfer at Pilot Ignition and Extinction of a Material", Fire Safety

Journal, 10, 1-10 (1986) .

[12] Thomson, H.E. and Drysdale, D.D., "Piloted Ignition of Plastics",

Proceedings of Fundamental Aspects of Polymer Flammability, Eds: Cox, G.

and Stevens, G., Institute of Physics Short Meetings Series #4, London,

England ( 1987 ) .

[13] Brown, J.E., "Report of Test on Combustion Characteristics of Fiber

Reinforced Resin Panels", FR-3970, U.S. Dept, of Commerce, National

Bureau of Standards (1987) .

28
[14] Carslaw, H.S. and Jaeger, J.C., Conduction of Heat in Solids, 2nd Ed.,

Oxford University Press (1959).

[15] Parker, W.J., "Development of a Model for the Heat Release Rate of Wood

- A Status Report", NBSIR 85-3163, U.S. Dept, of Commerce, National

Bureau of Standards (1985).

[16] Babraskas , V. and Krasny, J., "Predictions of Upholstered Chair Heat

Release Rates from Bench-Scale Measurements", Fire Safety Sci. Eng. ASTM

SP-882, Harmathy, T.Z., Ed., American Society for Testing and Materials,

Philadelphia, 1985, pp. 268-284.

[17] Kanury, A.M. and Martin, B.M., "A Profile of the Heat-Release Rate

Calorimeter", International Symposium on Fire Safety of Combustible

Materials, University of Edinburgh, UK (1975).

[18] Proposed Test Method for "Heat and Visible Smoke Release Rates for

Materials and Products Using an Oxygen Consumption Calorimeter", P 190,

American Society for Testing and Materials, Philadelphia, Pa.

[19] Kanury, A.M. , "Modeling of Pool Fires with a Variety of Polymers",

Fifteenth Symposium (International) on Combustion, The Combustion

Institute, Pittsburgh, PA (1975).

[20] Tewarson, A. and Pion, R.F., "Flammability of Plastics - I. Burning

Intensity", Combustion and Flame, 26., 85-103 (1976).

29
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Resin

Fiber

Potential

Source

Classification

Reinforcement

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Panels
TABLE 2

Ignition Delay Times for Composite Materials

Exposed to Various External Flux Levels

Ignition Delav Time (s)

Incident Flux (kW/m2

) Material ("thickness) 25 35 50 75

Koppers 6692T (25 mm) 263 120(10)* 60(2) 21

Dow Derakane (3 mm) 129 55 45(2)

Dow Derakane (25 mm) 390 187 55(2)

Corflex Panel (3 mm) 92(5) 54(2) 25

Corflex Assembly (37 mm) 122 70(0) 30(2)

Ryton Panels (3 mm):

Glass Mat (Chopped) 183+ 66 27(2)

Glass Mat Swirl 191(7) 97 28(5)

Glass Woven Mat Prepreg 154(7) 75 29(1)

Carbon Fiber: Woven Prepreg N.I. 88 38(3)

Lab. Epoxy Panel (3 mm) (a) 116 76 40

Lab. BMI Panels (3 mm) (a) 211 126 54

^Numbers in parentheses indicate range about a mean where duplicate

measurements were made.

^Duplicate tests performed only one specimen ignited.

N.I. = No ignition during a 600 s exposure.

la) Values taken from reference [13].

31
TABLE 3

Ignition Temperature of Six Polymers as Drysdale* Measured by Thomason and *

Temperature

Material ( °C)

Polyoxyme thylene 277 - 300

Poly(methyl methacrylate) -

a 298 - 328

Poly(methyl methacrylate) -2 a 276 - 317

Polypropylene 331 - 345

Polystyrene 337 - 369

Polyethylene 360 - 367

a: Poly (methyl- methacrylate) s from two different sources were used.

*Taken from Reference [12].

32
TABLE 4

Surface Temperature of Coated and Uncoated Graphite Fiber

Reinforced Composites 3 mm Thick at Pilot Ignition*

Resin/Coating Incident Flux

( kW/m2) Surface Temperature

f°C)

Epoxy 35 390

50 425

75 375

Epoxy/Nextel Prepreg. 35 390

50 400

75 400

Bismaleimide 35 515

50 500

75 455

Bismaleimide/Nextel Prepreg. 35 455

50 475

75 440

Bismaleimide/Nextel Dry 35 455

50 470

75 490

-'Taken from Reference [12]

33
TABLE 5

Minimum External Flux for Long Exposure Time and for 300 s Exposure To Cause Ignition Computed from the Regression of Ignition

Delay Time and External Flux

Material Regression MERF600

a merf300

»

Slope (kW/m2

) (kW/m2

)

Koppers 6692T (25 mm) -2.3 18 24

Derakane Panel (3 mm) -1.5 13 20

Derakane Panel (25 mm) -2.7 31 40

Corflex Panel (3 mm) -1.7 12 18

Corflex Assembly -1.9 15 22

Ryton Panels (3.2 mm):

Glass Mat (Chopped) -2.5 21 28

Glass Mat (Swirl) -2.6 23 31

Glass Woven Mat Prepreg -2.1 18 25

Carbon Woven Prepreg -2.1 20 28

a: Minimum External Radiant Flux necessary to cause ignition after 600

second exposure.

b: Minimum External Radiant Flux necessary to cause ignition after a 300

second exposure

34
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C c 1—

CO c i—

0) c cO cO (0 •pH •rH cfl 04 •rH CO CD •rH rH X rH rH E X E X 04 CJ X CJ CJ co O u rH o 4-J rH q2 04

5-1

X o 5-i

X o 3

CQ

X

X

X

X

X 5-i rH

0) cfl XI >

•rH

-j- in Ut <

36
Interval

Averaged

Rate

of

Heat

Release

of3

nun

Corflex

Panels

and

Panel

Assembly

(FR

EpoxyFiberglass

Composites)

cn

/«—

o o m o in o m m t o

LO 1 O t-H 1 o 1 in co o <t O co l o

CO 1 C*\ r-H 1 s—

T—1 W r-H sw' r-H

co /-N /-s /—X /—V /-s o 1 m m o o o o 1 m o o o o m m o in o 1 O r-H O 1-H CM CM 1 o m CNI LD cm in cm m r-H O r-H w r-H W rH '—

r-H vw' t—l ' r-H W rH W r-H

CO ^—

y

/-s x-v 2-x /-x oV O o ^ o o o o in in O m o o n o in in m m m

co co CM CM CO CM CM 00 CO ,—1 co av CO

CNI t-H w rH 'sw' r-H w r-H w r-H v—

r-H 'w' f—i

• r-H v—

r-H rH

—x

CO Lp) m ^-s o x—x in n o o

O r- O <t m o O 00 m in in rH n -d- O <f O <f o

o VO r-H vmO r-H in <j\ 00 r-H mo CO r-H <T i in rH r-H v£> oo H r-H 'w' r-H '—

r-H w r-H v—

r-H W T—1 S '' T—H sw" r-H N>—

r-H

t-H

*

co /-N /-N /^N /-x ^x /^-X x—

o o m m m o n o o O in o o o o oo in r-H m cm n c in <f m oo m

CM in t-H r*- r-H On CM 00 r-H r-H CM <r t-H <T r-l in r-H 00 r-H 00

r—r-H ^ r-H N—r-H W r-H '—

CM w rH sw/ r-H r-H ' rH w r-H

co o o m m m o o o O o O r^ r-H r^ LO On CT'> LO r-H r-H r-H r-H CM rH t-H rH r-H r-H

<Me

l

m o o m m o o in m

3 co co m m CO n m 2

?x

r-H t-H r-H rH r-H & 2 2 2i X)

r-H r-H r-H r-H r-H E E E E s

a> a; a; Q) 0) <d 0) cu 0) 0) C c C C G co co CO co C/3 CD 03 03 03 03 03 co co CO co cn

r-H CL, Cl, cu CL, CH < < < C <

a

E X X X X X X X X *

03 a> CD Q) d) <d <d <u <d <u 0) on r-H r-H r-H r-H rH rH r-H rH r-H r-H UH CH Mh <4H Ct-I 2 Hn 4h mh 4-1 Jh J-l JH LJ J-l U u !h Jh J-l O o O O O O o o O o O o O O CJ CJ o cj CJ CJ

u

0) 2 o <r in r-H o lO p*- in <r E co r-- CO co lO <r co co in n

3 r-H t-H in m r-H rH m m r-H r-H 2 t-H r-H r-H r-H r-H r-H r-H rH r-H r-H

37

^Values

in

parentheses

are

averaged

over

the

previous

60

s

interval.
Interval

Averaged

Rates

of

Heat

Release

of

25

mm

Thick

Dow

Derakane

Pump

Housing

(Vinyl

Ester

Epoxy-Fiber

Glass

Composite)

co o o in in o in o m o o o o in in Csl o <3* in CM

CO vo i—

<r

T

—

40 r—l r—l 40 r—l r^ r—l CO r—

r—l r—l r—l r—l

M ' i—

INE co /s /—N xs /-s

—

\ r—l in o o o in 3 O o r—

m o o VO in in co in co

,X

O oo r—l r—l CO r—l 00 rH vo r—l 00 r—l co r—

r—l r—

'•w'

r

—W i—i r—i

0)

CO

ca

03 co /~N /N /—>4 /-s

r—l r—l

n o o O o

03 o o r—l

m r—l o in in vO in o in

03 <r o r—l

m r—l 40 r—l ONT

—

r—l o r—l CM Csl 'w' r—l s-^ i—4 S^ r—l ' i—i Sw' CM s^

4-3 03

03 X,

CO s /^v /—

/~s r—l 44 o o in in o o O o o co o CO o o o vo in Oh >

oo Csl r—l i—40 i—i 1—1 r—l oh 1—1 r—i i—l 34

03

r

—

CsJ 'w' r—l s-/ 1—1 Sw' Csl Sw' r—l 'w' CM Sw' 03

4-3 4J 0) c

cd • 1—1 *

03 co /T\ /^i /~s /T\ /^s /-

—

co

W

O o o in

O in

03 o in i—

n vO o in in o in Oh in o o

44 CM in r—l On r—l r—l CM CM o i—l CM CM 40

03 i—

Csl 'w' r—l Sw' i—4 s*/ CM s^ CM CM Sw' > co < 3o

•1—

>

CO 03 m n o o o 44 o ov Csl 04 i—i CL CO CM Csl r—

CM CM CM

03 -C

4Jgou

4-1

INP3XI

1 £tl

Ln

on olO

Om

m

r-~ in in

r» r--

4-3 c

03E

•r4 34

44 03

03

X Csl o o i—i 00

CL E r^ in 00 in in in X 3 i—i in o i—i i—i r—i Ld Z r—l i—i 1—1 i—i r—i i—i

X!

cu40u

<u>

0}

a>

>-i 03

CO

a)CO

0) -C

•ue

0344

03ac

co

033

f—

03 >

-M

38
TABLE 10

Interval Averaged Rates of Heat Release of 3 nun Thick Laboratory Samples of Epoxy-Graphite Fiber

Composite Panels 3

Experiment Flux

Number (kW/m—

)

Average Rate of Heat Release (kW/m—

)

(60 s

)

(120 s') (180 s') (240 s') (300 s) (360 s)

35 150 155 120 95 75

(160)* (50) (20) (-0)

2302 50 185 170 135 105 85 75

(155) (60) (15) (10) (10)

2311 75 210 190 145 150 100

(165) (60) (25) (-0)

(a) Taken from Ref. [ 12] * Values in parentheses are averaged over the previous 60 s; interval.

39
Results

of

PostIgnition

Averaging

of

the

Rate

of

Heat

Release

of3

min

Thick

Ryton

Panels

(Reinforced

Poly

(phenylene

sulfide))

cd rv o in 1 o v X—

uo

VO o CN 1 o CO

O o uo o UO o o uo uo o o

co CN '•w' CO 'w'

O o 1-H r-H uo 'w' CN

t—r-H 'w' r-H

<Me CD /-s uo /-N 3 o o 1 o /-v o o o o CN 1 o r-H UO o uo o o o o uo vO uo uo 'w co CN On r-“1 r—1 i-H r-H S-/ uo CO r-H

r—

1 r-H 'w' w' r-H '•w' <u

cdct

CD i—

uo /-s o o 1 CO uo ~s o o

OS o 1-H 1 UO r-H o o UO o o o uo VO uo CO CN CN '—

CO CO CN i—

t-H uo uo CO r-H •u r—1 T—

rH 'w'

cfl <u Xo CD x—v /-v /-s /-S 1 UO UO uo UO

CD o o uo 1 O r- o UO CN o X"*

o o vO UO CO

•u 00 CN 'w' 'w' co o r-H r-H UO 11 o uo 'w' r-H r-H

CD

r—

i—

i-H N-^ r-H 'w' OS

0)

t>j: CD <

CO /-V /*s /-s

S-J o o 1 o UO /-V uo o

0) CSI o r-H 1 uo vO UO UO Ov o UO o o uo uo o > r—

CO V-/ vO 'w" r-H Ov r-H 'w' 11 'w' r-H r-H < r-H r-H

CD hH o o uo o O o UO uo UO

v£3 uo 2 r-H o CN

V CO

r-H 1—1

HNE X \ LD o uo uo UO UO o uo d 3 co uo co CO UO

r-l PS

IX -HuC

<d x> E CD

CD S •u O cD X T3 S o 0)

x XH CL. r-H

cd c ex

u

XI •rH o •rH •rH cd x 3

IX QSu cn

4-> e

<dE

•rH 1-1

1-1 01

CD

X uo VO UO r-H cc CO UO CX E C30 00 r^ 00 00 00 x d CO CO UO CO CO CO CO UO CO w z r-H r-H r—

i-H r-H r-H r-H r-H r-H

40

1382

75

90

110

110

130

120

105

(130)

(115)

(180)

(100)

(30)
TABLE

11

(Continued)

c/3 in o m m m o

VO

VV in 'w' oo

CO

CME\ C/3 o 3 rH O m in in 5—1 in n

o V V m ON

co

05

COCO

<u I—

C/3 /-s

0) in

OS

O uo in

m o

<rVV in o 4-> CNl T—C

CTJ <D I

4-1o C/3

<u

O in

m o vO in

•u CO

VV in ON

CO 5—1 a

<05 b£ c/3 c0 /-S

5-i

OO

<D CNl in in in VO o > 5—1 Nw' On <

CO o o m

m U~l vO 5—J CO 00

X

-He

in in

O

n 3 cn CO m

rH

ta

-45

•Uc

0)E

OJ

U o CO

5-1 s O

5-1 4-1 c

<U c 0) X1 -H >

•r-C CL) o

Ctt OS 3

4Jc

0)E

•H 5—i 5-1 0)

<u

x ON o On

a E 00 On X 3 CO CO

m CO

W 2 !—

t—H 5—1 r-l

/-N /'-N in in in o CNJ i ii O CNl O CO o

oo >*w' 1 1i CO 00

/—N /v /-N o o in

O vO i i O CNJ o CO o

ON | i 00

w ON

O5—1 in

m 1—1 * i uo co o o in

on

W 1 • CTn S-' o5—

o5—1

O o5—1

5—1 1 i in o o oCO in ON ^ 1 i r—

X CNl 5—1 CNJ rH —' 5—1 '

' 5—1

/~s in y—

in 5—1 O in 00 i i1 o 1—1 O m o

00 v—' i i1 o*\ 'w' CM i—

CO

i—i

w 5—1

1—1 M

O o in o

oo

X 00 o5—

in in in o in in CO CO in

co

5-1 a/ -O

•i—i X

•u

cfl <D s •u

•i—(

C -C

CU CL > C53 o 5-i 2 CJ

CO 5—1 CNJ vO o <r

CO ON On 00 00

CO CO CO in CO co

5—1 5—1 5—1 5—1 5—1 5“l

41

N. I

=

No

Ignition

^Values

in

parentheses

are

averaged

over

the

previous

60s

interval
Results

of

Post-Ignition

Averaging

of

the

Rate

of

Heat

Release

ofa3

nun

Thick

Laboratory

Sample

of

BMI

-Graphite

Fibers

Composite 3

co o O o ^0 in

m in vO OV rH CJN rH o 04

rO r—1 rH

CTJ x-* >

CO

u

/-s /—

<d

O LO o o in

m o 4J o o rH CO 04 CO c

co rHH rH •H

to o

CO vO e /-N /-s /-s \ o o o o o in in co 3 CM ON co ON 3 X CM rH rH rH o

•H> z <D •O' x- M

C0 /*

CX

cd o o m

bC o m <r

m

mm

m CD oo co f-H rH vo rH x

M rH rH

V-/ rHM ' i—

4-> 0)> E < O

/—N < u cn /-s 4-4 o o o o O co LO r>* o o T3 04 co rH rH 04 04 rH r—

—

H rH 'w' OO3M

0)>

<0 cn

lPi o o , , cd o O 04 CM M

kD r—

rH rH r—

CO 1 ' co

<d a) o (0 -H c CD IM <u X

x e S-i 4-1 3 'N LO o m a) c

<-4 S co uO o- cm a) IX X CD M —

oS cOcx E

4-1

O c c M •H

0) CM e co •H c <D

!-i <D <d 3

<u

X vO CO CO

X (—* ex e On o rH <0 CO X 3 Csl CO CO H >

Cxj 2 04 04 04 *

42
Results

of

PostIgnition

Averaging

of

the

Rate

of

Heat

Release

ofa2-

Ply-Reinforced

Vinyl

Poly(styryl

pyridine) -

BMI

Resin

Experimental

Composite

•cr

<dw

cfl

S-4 <d

!> < o r—H vO 1 1 'w' CO 1 1 cnrH

co o m o il i-

O V—

1 'w' co m 1 in V r—

CO o o o (1 r—

1 CM m 1 m V T—

CO o m o o il V rH

co ''w' Vw-' >—

(—1 LO

m > * S-l CO /^*S /*n /-s CD m m m •U o V V rH c

CM •r-l rH m m ON

rH co o

VO

co o

vo o i""

m

(—"I Osl

co3O

•i-l >

0)

5-1 CD

CD u£ou

4-1

T3

<DM3

)-i (D>

cfl

a)p

cfl

UG

CD£

•iH

u

u <D CD £>

CDH

X 3 w Z

00

vo

VO co

<r

in

to

0)

to

CD XUC

CDCl

ct) aa

•i

—

to

<D3

r-H

ctJ >

-X

43
Comparison

of

Inferred

Flammability

Indices

of

Composite

Materials

CM

CXM o E

Efa 3 CM

fa fa

fa H S

OO CM

r—1 CM

oo oo

<—I CM

+1 oo i—i m oo oo CM CO CM CM CM

HCME3

fa o

CO

cnCM o

o

o

O cn fa r*.

ln o i in in <t

i i

cn

fa

o

CM+1

<

1—

CO rH ON co v£> 00 VO

CO • H o rH o r—

o r—1 rH rH <H tH

CME\

CTN 3 Csl O

fa

-—

+1 +1

4-J

4-1 CM CM

® t—

rH

O

+1CM O O

I CM CM

CO

cO O CM O CO

i—l CM CM O i—

+1 +1 +1 +1 +1

U0 CM CO CO CO

CM CM CM CM CM

Q 1

H & £ S C

CM £ CO £ Q) On CO r—

>

CO M •• a> CO fa o

CO CO c r—

(

cO 3

fH rH cfl a) S fa fa C Q) <1) fa C C/5 cO <u o c c T—

fa s S fa a)

' r—

£ rH >N fa QJ 0) •H 00 Q £ PL( fa X ^ c (fa 1—

c fa fa fa s o E i—

ct) (fa 5-1 aj ex cd fa

(fl m X X 0) (fa E S fa O fa > Cfl S a)

5-i Csl a; a) c/) fa CQ fa 5 o 5-1 >

a) rH rH C/) CO c (_> CO 3 O C

fa 4-1 4-1 <d . ^ o

(fa 5-1 5-1 fa fa fa o O O tO fa CJ O fa fa fa

44

TSI

=

Thermal

sensitivity

index.

ESI

=

Extinction

sensitivity

index.
TABLE

15

Average

Yields

of

Combustion

Products

for

Various

Types

of

Composite

Materials

on r-H vo t-h

<0 O r—H r—I r—I r—

o\ o o o o o

ol

p"- r— co co r^

oo vo r^- O O cm o O

ON ON <f

r—I O r—

OO O rH r-H CM O r—I r-H t—I r—

rtj o o o o o

o| . . . . . ol o o o o o

H n in <f n

t—i r—1 0O pH rH O O pH o O

o o o o o

<3-0 0 O I-I o

o o o

no in in

<f <N o o o

o o o

rO CN O on -j- m

O pH pH

oo m <t CO pH r—l o o o

a

c/5 C

o

42

CO

CJO

Sh TS>\

O O no to

I—I <-H O O O

o o o o o

O' 00 00 pH o o o o o • • •

•

(I o o o o

CM CN H

o o o

o o o

CN CM rH o o o

o o o

ON <f m o o

o o o

o o o

w

c Mo M

•H e o o o Ln

•u CO o i''. o

o NO m O' CM c C/5 r-H r—

r-H •H 03 •u 0) X S-i W <

o o o m o r- O O CO O'

in no no oo

p-l CN CN H H

lO o o o

o O' o 00 1^- 00 CM

o o o

CO o NO m no r-^ o o o

co O'

CNI NO <r

cff>

cn t—

o

CO HIo .u H

NO O' I—l r-~ o pH (—1 CN

NO CN NO NO

in in in in m

o O'

pH CN pH

<f <f NO CN CN CN CO <f CN CN CN CO

co •H

Oi m t—

r-H NO o <t <r co in ON co vo vO vO U 05 vo vo NO NO in m vo m vo m m m

•Hc

hH

C/5

cfl S

<1* <r <1-

-H X

3

r—

U-4

CM£

Nj

44 m LO m o LD LO m o O in m o in in O in m o m

CM CO CO m CO CO m m CO m 0- CO in CO m

r-H C CD C/5 o 3 tH /P—N, •H cO 05 u Q PL X c 03 0 o C/) i—

C/5 CO S

05 X Oh f”H s rH PL U H m VO vO CD o in r-H U3 (D cq 05 rH m m r-H

CD CN ON CTn 00 ON rH co CO CO VO 3 3 c !n oo 00

CL O' o o o o MH r-H r-H in m r-H cO CO o •rH CO m CO

Cl no r-H r-H r—

r-H H r-H rH rH r-H r-H 42 PL 42 PL u £ r-H r-H r-H O NO O cQ cO >*, on

341 O p4 rJ oP

45

(a)

Ratio

average

of

mass

generation

rate

to

the

mass

loss

rate
0)

r

—

jo

03 H

CN 4-3 o c u 03 \ 34 W3 0 03 0(3 <44 \ T3 <44 (N C •r-l E 1 03 Q -

o

CM r—l - 44 o X

(SI 03 o •w o \ u 03 0 \ r4 o 03

(N

*i4>4

03 44

03

03O4 o 03

03

C_> s \o 03 03

03>4

34 o

3-1

44

•l—l 03 (SI o O

rO o <4-1 OrE

r-43

ru\

03

O

u

T3 o 44 X f—^ 03 44

>0 W

03

•i—

>|

<44o

03

03 03 00 Or

03

!-i

H

03 CM > 03 o

<d 3 u O

<44 •H o O 34 u

o:

O >

0O

M ^ H (J\

1-4 i—I O (-4

O

HH sf in to

r-1 OS <T U~l (—

r-l

OOOO

os os o O O O .-4

O o o o o o

ro

nh cs <r 4 Oi CO 00 <f lO o o o o o o o o o o o o o o o o o

CM (Tv cn T—I r-l O O O o o o o

r—I Csi ^3 r—I r—4 r—

o o • o o o - • o . . . O O V o o o V

r-l (N in IN (N

N

H <f OOOOO O r-l o

on ro r-

o o o

OOOOO o o o o o o m <T rO o o o o o o

l/S

r-4 r—

o o o o o oV

CO r-l ON CO r—I O O O O • r-l u 4

03

O

03 <44

X3

r—l Ui

H(SIE\

-X

in

m its o m

cn to cn

n i

in LO

O

O

m u~l

O <n

mm in

m rs on in rin o m

cn in

lo o m

com r-»

03C

03

O-i >sX

r—l

O 03 4-1 03

03 03

X Or 44 2 44

•r—l 4 03

W .4 CO •1—1 4 03 H rH X X

03 Or Csl

m <44 o m 1 1 • Or Or

44 Or OS CTn ON OO ON 4 CO r- CO CO VsD

X 03 -O 03

03

O SO o o o o o i—i r—l LD lD r—l 03 4 03 4 X X3 SO r—l r—l I—

T—

o i—

r—l 1—1 T—

r—l

J e> l-J C3

46

PPS/Chopped

Mat
Figure 1. Schematic Representation of Cone Calorimeter

47
IGNITION

DELAY

TIME

(s)

Figure 2. Range of Ignition Delay Times as a Function of External

Radiant Flux for All Composites

48
IGNITION

DELAY

(s)

1000 F

100 -

10 L10

Figure

T t r

Koppers

Corflex

panels

Slope

i iiii

EXTERNAL IRRADSANCE (kW/m2 ) 100

Ignition-Delay Time for Two Composites as a Function of

External Radiant Flux

49
RATE

OF

HEAT

RELEASE

(kW/m

Figure 4. Effect of Irradiance on the Rate of Heat Release from a 25 mm FR Polyester/Glass Composite

50
RATE

OF

HEAT

RELEASE

(kW/m

CM

Figure Effect of Irradiance on the Rate of Heat Release from a

3 nun FR Epoxy/Fiber Glass Composite

51
Figure 6. Effecc of Irradiance of the Rate of Heat Release from

from 3 mm Poly (phenylene Sulfide)/Fiber Glass Composite

52
MASS

LOSS

RATE

(g/s)

0.5 -r

0. 4 - Brominated phthalic polyester-fiberglass composite

75 kW/m2

50 kW/ m2

35 kW/m2

25 kW/ m2

150 300 450 600 750 900

TIME U)

1050 1200 1350 1500

Figure 7. Effect of Irradiance on the Mass Loss Rate from a FR Polyester/ Fiber Glass Composite

53
MASS

LOSS

RATE

(g/s)

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0 50 100 150 200 250 300 350 400 450

TIME (s)

Figure 8. Effect of Irradiance on the Mass Loss Rate from a 3 FR Epoxy/Fiber Glass Composite

500

mm Thick

54
MASS

LOSS

RATE

(g/s)

Effect of Irradiance on the Mass Loss Rate from a 3 mm Thick Poly (phenylene Sulfide ) /Fiber Glass Composite

55
'

(kW/m

2)

Average q' as Function of Time After Ignition

Interval (60s) Averaged q* After Ignition

POST-IGNITION TIME (s)

Figure 10. Average q as a Function Time After Ignition of Irradiatively

Heated Koppers Dion 6692T Composite ( FR Polyester/Glass)

Panels

56
-

(kW/m*)

1

"(kW/m

2)

Average q' as a Function of Time After Ignition

Interval (60s) Averaged q* After Ignition

250

(b)

r 1 1 75 kW/m2 *—

200

150

35 kW/m2

^

\ \

100

r

— T

ji

50

0

^

50 kW/m2 — -•

i i i 0 100 200 300 400

POST-IGNITION TIME (s)

Figure 11. Average q as a Function of Time After Ignition of

Irradiativel Heated 3 mm Corflex (FR Epoxy/Glass)

Panels

57
•

(kW/m

2)

q'(kW/m

2)

Average q* Versus Time After Ignition

Interval (60s) Averaged q* Versus Time After Ignition

Figure 12. Average q as Function of Time After Ignition for

Irradiatively Heated 3 mm Ryton Panels ( Poly (pheny lene

sulfide)/Fiber Glass)

58
Figure 13 Average Rate of Heat Release Up to 60 s Pnci- t Several Centres as a Function ofVZZt lZ

^ ^

59
GAS

YIELD

(kg/kg)

Figure 14. The Effect of Irradiance on the Production of C02 from 25 mm

FR Polyester- Fiber Glass Composite

60
GAS

YIELD

(kg/kg)

Figure 15. The Effect of Irradiance on the Production of

FR Polyester/Fiber Glass Comnosite

—i

1500

CO from a

61
NBS-I 1 4A 'REV. 2-80

U.S. DEPT. OF COMM.

/'BIBLIOGRAPHIC DATA

1. PUBLICATION OR

REPORT NO.

j

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

SHEET (See instructions) NBSI R-88/3788 [ _ __ March 1988

'I 4. TITLE AND SUBTITLE

Cone Calorimeter Evaluation of the Flammability of Composite Materials

5. AUTHOR(S)

J.E. Brown, E. Braun, and W.H. Twilley

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

— — ————

7. Contract/Grant No.

8. Type of Report & Period Covere,

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

U.S. Dept, of tne Navy

Naval SEA Systems Command (NAVSEA 05R25)

Washington f DC

10. SUPPLEMENTARY NOTES

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

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

bi bliography or literature survey, mention it here)

A study was undertaken to evaluate the fire performance of composite

materials using the cone calorimeter as the bench-scale method of test

simulating the thermal irradiance from fires of various magnitudes. Five

parameters were derived from the calorimetery measurements to characterize

the ignitability amd flammability of the composite materials. Three of the

parameters are, to a large extent, empirical since radiative heat losses from

the samples were unknown. These parameters are; 1) minimum external radiant

flux (MERF) required to produce pilot ignition in a predetermined exposure

time; 2) thermal sensitivity index (TSI) which indicates the burning intensity

dependence on external heat flux; and 3) extinction sensitivity index (ESI)

which indicates the propensity for continued flamming combustion without an external heat flux. MERF valves at 300 s for 3 mm composites panels of a FR

epoxy resin and a poly (phenylene sulfide) (PPS) resin composites were about 18

and 28 kW/m2

, respectively . The TSI of the PPS resin composite had the

greatest dependency on external flux. Additionally, the ESP of the PPS

composites was the only one to indicate an external flux requirement to

sustain combustion during the first 60 s after ignition. The other two

parameters determined were yields of gaseous products of combustion and

average extinction area, a, normalized to the C02 yields.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) combustion; composite materials; cone calorimeters; extinction; fiberglass

resins; flammability; heat release rate; ignition; resins; smoke; thermal

decomposition

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

| X 1 Unlimited

6 8 | | For Official Distribution. Do Not Release to NTIS

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

15. Price 20402.

[Xj Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $13.95

USCOMM-DC 0043 -P *