JUTS' M? -7 7- IV CL, FAARD-77-47

"

STUDIES OF THE FLASH FIRE POTENTIAL

OF AIRCRAFT CABIN INTERIOR MATERIALS

Michael I. Manka

Henry Pierce

Clayton Huggett

DECEMBER 1977

FINAL REPORT

Document is available to the public through the

National Technical Information Service

Springfield, Virginia 22151

Prepared for

II. $. DEPARTMENT OF TRANSPORTATION

FEDERAL AVIATION ADMINISTRATION

Systems Research & Development Service

Washington, D.C. 20590
NOTICE

The United States Government does not endorse

products or manufacturers. Trade or manufacturers’ names appear herein solely because they are considered essential to the object of the

report

.

NOTICE

This document is disseminated under the sponsorship of the Department of Transportation in the

interest of information exchange. The United

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contents or use thereof.
Technical Report Documentation Page

1 —i . Report No. 2. Government Accession No. 3. Recipient’s Catalog No.

FAA-RD-77-47

4. Title and Subti tie Studies of the Flash Fire Potential of

5. Report Date December 1977

Aircraft Cabin Interior Materials 6. Performing Organization Code

8. Performing Organization Report No.

7. Author's) Michael J. Manka, Henry Pierce, Clayton Huggett NA-77-180

9. Performing Organization Nome and Address 10. Work Unit No. (TRAIS)

National Bureau of Standards

Washington, D.C. 20234

11. Contract or Grant No. FA67NF-AP-21

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address Department of Transportation

Federal Aviation Administration

Final

August 1975-September 1976

Systems Research and Development Service

Washington, D.C. -20590

14. Sponsoring Agency Code

15. Supplementary Notes This work was supported in part by the National Aviation Facilities Experimental

Center (NAFEC) Atlantic City, New Jersey 08405. Mr. Constantine P. Sarkos was the

NAFEC project manager.

16. Abstract This is the third in a series of reports describing work carried out under the joint

sponsorship of the National Bureau of Standards (NBS) and the Federal Aviation Administration (FAA) to develop a method of assessing the flash fire potential of materials found in aircraft cabin interiors.

The flash fire cell described in the previous report was modified further and used

to evaluate the flash fire potential of a series of 24 typical aircraft cabin interior materials. Flash fires were observed in the apparatus at fuel loadings as low

as 0.23 gL~l.

A minimum energy principle was proposed to characterize the flash fire behavior of

the complex mixture of fuels derived from the pyrolysis of organic materials. This

principle states that a flash fire is possible when the potential combustion energy

content of the pyrolyzate-air mixture exceeds approximately 425 cal L“1

.

A variety of experiments was performed to provide support for the minimum energy

principle. The results were in general agreement with predictions, but the accuracy

of the measurements was not good enough to permit detailed conclusions.

Oxidative pyrolysis plays a significant role in the formation of the fuel-air mixture

in the flash fire cell. Particulates contribute to the creation of flash fire

conditions, but they present a difficult measurement problem.

17. Key Words Aircraft Materials

Combustion Products

Flash Fire

18. Distribution Statement Document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22151

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21- No. of P ages 22. Price

Unclassified Unclassified 37

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

PREFACE

This is the third in a series of reports describing work

carried out under the joint sponsorship of the National

Bureau of Standards (NBS) and the Federal Aviation Administration (FAA) to develop a method of assessing the flash

fire potential of materials found in aircraft cabin interiors.

This work was supported in part by the FAA's National

Aviation Facilities Experimental Center (NAFEC) , Atlantic

City, New Jersey 08405 under FAA/NBS Agreement No.

FA67-NF-AP-21 . Mr. Constantine P. Sarkos was the NAFEC

project manager.

iii
TABLE OF CONTENTS

Page

INTRODUCTION 1

Purpose 1 Background 1

EVALUATION OF THE FLASH FIRE POTENTIAL OF AIRCRAFT CABIN

INTERIOR MATERIALS 2

Materials 2 Flash Fire Cell 2 Experimental Procedure 2 Test Results—Flash Fire Potential 3

INVESTIGATION OF CONDITIONS WHICH CAN LEAD TO A FLASH FIRE .... 4

The Minimum Energy Principle 5 Experimental Materials 7 Methods of Experimental Measurement of the Energy Content

of Pyrolysis Gases 7 Measurement of Energy Content of Pyrolysis Gases in the

Flash Fire Cell 8

Probe Pyrolysis Experiments 9

Sample 8 9

Sample 16 10

Sample 38 10

Sample 42 10

Summary of Energy Content Measurements 10

Gas Analysis Experiments 11

SUMMARY AND CONCLUSIONS 12

REFERENCES 13
LIST OF FIGURES

Figure Page

1 Modified Flash Fire Cell 24

2 Typical Experimental Run where Sample Pyrolyzates

Produce a Flash Fire 25

3 Pyrogram of Sample 8 in Nitrogen 26

4 Pyrogram of Sample 16 in Nitrogen 27

5 Pyrogram of Sample 38 in Nitrogen 28

6 Pyrogram of Sample 42 in Nitrogen 29

LIST OF TABLES

Table Page

1 Materials Evaluated in Flash Fire Cell 14

2 Flash Fire Test Results 16

3 Ranking of FAA Samples which Flashed 17

4 FAA Samples which Failed to Produce a Flash

under the Test Conditions 17

5 Results of Composite Samples 18

6 Lean Limit Mixture Heats of Combustion for

Upward Flame Propagation of Organic Fuels 19

7 Properties of Polyurethane Foam Samples 19

8 Results of Flash Fire Experiments for Samples

8, 16, 38 & 42 20

9 Results of Energy Measurements of Flash Fire

Experiments for Samples 8, 16, 38 and 42 21

10 Energy Measurements from Flash Fire Experiments 22

11 Comparison of Energy per Unit Volume at the Minimum

Mass Limit as Determined by Various Methods 22

12 Gas Analysis Results from Flash Fire Cell Experiments . . 23

v

INTRODUCTION

PURPOSE

The purpose of this project was to develop a method of evaluating the

flash-fire potential of aircraft cabin materials, to evaluate selected

materials and conduct additional studies to gain a more complete understanding of the phenomenon of flash fire.

BACKGROUND

Accidents have occurred in which an impact-survivable crash landing

of a passenger aircraft was followed by a rapidly propagating fire in

the aircraft cabin, causing extensive casualties among the passengers

and crew before evacuation or rescue could be effected. While such

events are fortunately rare, their catastrophic nature has focused attention on developing an understanding of the mechanism of these cabin

"flash fires" and developing means for their control.

Previous NBS reports, dealing with flash fire studies, described

exploratory experiments in which a flash fire cell was constructed and

used to make preliminary comparisons of various polymers and to assess

the usefulness of the apparatus used for measuring the flash fire potential of materials (reference [1]). An analysis of the pyrolysis

gases and smoke evolving from thermal decomposition of polyurethane foam was also performed. The results indicated that smoke was playing a significant role in producing a flash fire since a flash did not occur when the smoke was filtered out. A later study [2] refined the technique

of using the flash fire cell to assess the flash fire potential of materials. In that work several variables, including cell orientation and oven temperature, were studied and an experimental procedure was established. The important parameters in assessing the flash fire potential

of polyurethane foam were found to be, (1) the minimum mass of sample

per unit volume needed to produce a flash fire, and (2) the minimum

temperature the sample needed to reach in order to produce a combustible

pyrolyzate/air mixture. This minimum temperature was found to be about

380° C for polyurethane foam. The minimum mass depended on the chemical

structure of the sample and its decomposition products.

In the present work the flash fire cell was further developed and used

to evaluate the flash fire potential of a series of aircraft interior

materials. Based on a minimum gas phase energy hypothesis, experiments

were carried out to investigate the conditions which could produce

flash fires.

1
EVALUATION OF THE FLASH FIRE POTENTIAL OF AIRCRAFT CABIN INTERIOR MATERIALS

MATERIALS

Twenty-four typical materials found in aircraft cabin interiors were

supplied by NAFEC for evaluation. A listing of these materials, their

description and usage are presented in table 1.

FLASH FIRE CELL

The flash fire cell described previously [2] was modified to provide

greater flexibility in operation. A sketch of the present cell is shown

in figure 1. The body of the cell was constructed from a length of 5 centimeter (cm) inner diameter I.D. pyrex glass pipe. The volume of the

cell was increased to 1.69 liters (L) . A magnetically driven stirrer

was added "to improve mixing of the pyrolyzate with air. Thermocouples

were inserted through the sampling septums to detect the passage of a combustion wave and allow an estimate of flame speed. These septums were also used to withdraw gas samples for analysis by means of a gas

tight syringe. The polarographic type oxygen probe, retained and mounted

in a plastic plate, was held in place at the bottom of the cell by a set

of springs. This spring loaded plate provided a pressure release mechanism in the event of a pressure buildup during pyrolysis or a flash fire.

The entire cell was designed for easy disassembly and cleaning between

experiments

.

The manual ignition control was replaced by an electronic system which

provided precise and reproducible control of the spark duration and the

interval between sparks. The igniter was constructed from platinum electrodes with a 6 millimeter (mm) spark gap. A 10 thousand volt (kV) spark

was used for ignition of the pyrolyzate/air mixture. This source was sufficiently strong to ensure ignition of any combustible mixture.

EXPERIMENTAL PROCEDURE

A weighed sample of the material to be evaluated was placed in the cell

as shown in figure 1. The furnace, which had been preheated and thermostated at' a preselected temperature, usually 500 °C, was placed over the

side arm containing the sample to initiate pyrolysis. Preliminary experiments had shown that a temperature of 500 °C was sufficient to bring

about complete pyrolysis of most organic materials.

Sample temperature, as measured by a chromel-alumel thermocouple, and

oxygen concentration were recorded continuously during the experiment.

The sample experienced a heating rate of about 200-250 °C per minute,

similar in magnitude to that which would be encountered in a fire

exposure

.

2
With the onset of pyrolysis the ignition source was activated to give a spark of one second duration at regular intervals. The sparking was continued until a flash occurred or pyrolysis of the sample was complete

and it appeared that no flash would occur. A record of a typical experiment in which a flash occurs is shown in figure 2. The occurrence of a flash fire could be detected by a visibly luminous flash, a sharp deflection in the oxygen concentration record, or a sudden increase in

temperature indicated by the thermocouples in the cell.

Initially a sample weighing about 1 gram (g) was tested by the procedure

outlined above. If no flash occurred, the sample size was doubled for

the next trial. If a flash did occur, the sample size was suitably re- duced for the next trial. In this way the minimum sample mass which

would produce a flash in the apparatus was established with reasonable

accuracy in the course of a few trials.

Because of the limited quantities available, the minimum mass could not

be established for some samples. In these cases the largest sample

tested was reported. Some materials were considered to have a low

flash fire potential so they were not studied further. Due to the

limited volume of the sample holder, some of the low density composite

panel materials could not be tested in their original configuration.

These materials were separated into their principal components and each

component was tested separately. The minimum mass of the composite

material was then calculated by the formula

min. mass

-i -1

where m^ is the minimum mass of component i and x. is the weight fraction

of component i in the composite.

TEST RESULTS—FLASH FIRE POTENTIAL

Results obtained with the 24 cabin interior materials tested by the

procedure described above are summarized in table 2. In cases where

a flash was obtained, the minimum mass per unit volume is given. Where

the sample failed to produce a flash, the largest sample tested (g/L)

is given and the symbol (>) indicates that the minimum mass will be

greater than the quantity listed. For the most part, failure to establish a minimum mass was due to a lack of sufficient sample, but in the case of the fiberglass samples (27, 66 and 115A) the sample size was limited by the size of the sample holder.

3
The maximum temperature reached by the sample and the oxygen concentration achieved at the time of flash or the minimum oxygen concentration

in the case of samples which did not flash are also listed in table 2.

Some variation was observed from test to test, therefore, the range of

sample temperature and oxygen concentration are presented in the table.

It should be noted that about half of the samples did not produce any

flash even for relatively large sample sizes. This is not surprising

since these materials are composed of relatively inert or thermally

stable components, such as fiberglass, or flame resistant polymers, such

as Nomex. Both the polyvinyl chloride (PVC) foam (86) and polycarbonate

(32 and 111) samples did yield flashable mixtures. The two flameretardant urethane foam samples (143A and 143C) yielded quite different

minimum mass results. Sample 143C is considerably more resistant to

flashing whereas in sample 143A the flame retardant appears to be

relatively ineffective in preventing a flash.

The samples which produced a flash can be ranked according to the minimum

mass criterion as shown in table 3. The poly (phenylene oxide) and

polyether -polyurethane samples (117 and 143A) were the most easily

flashed. Samples which failed to give a flash under the test conditions

are listed in table 4 in the order of increased sample size tested.

This does not provide a ranking since there is no way of determining

from the present data that these samples approached the minimum mass.

At best, it can only be said that their flash fire potential is considerably lower than the first 10 materials listed in table 3. Additional

testing with larger samples would provide further differentiation.

Some composite samples were directed into their different components

and each individually tested in the flash fire cell. These included

samples 1, 2, 14, 37, 50, 61, and 67. The results of these tests are shown in table 5. The weight fraction of each component is also given.

The Nomex core and some fiberglass facings were not tested as they were usually destroyed during the separation process. It was expected that

these materials would not contribute significantly to reducing the mini- mum mass and they were therefore excluded from the calculation of the

total minimum mass.

INVESTIGATION OF CONDITIONS WHICH CAN LEAD TO A FLASH FIRE

A flash fire may be described as the rapid propagation of a combustion

wave through a gaseous fuel-oxidizer mixture. In the present context

the fuel consists of the partially oxidized pyrolysis products from the

cabin interior materials. The oxidizer is oxygen from the air, either

that present in the cabin originally or an additional supply introduced

through cabin openings. The fuel may be generated by a slow smoldering

combustion where the products mix with the cabin air to form a combustible

mixture but the temperature is too low to cause ignition. An independent

ignition source may then trigger the flash fire. Alternatively, the fuel

4
may be generated by open flaming under conditions of limited oxygen

availability (excess pyrolyzate [3]). In this case a fuel rich, oxygen

deficient, mixture will be generated which can burst into flame when

external oxygen is admitted.

The propagation of a flame through a fuel-air mixture has been studied

in considerable detail [4]. It is found that a well defined minimum

fuel concentration, called the lower or lean limit (LL) , must be ex- ceeded for the flame to propagate. As the fuel concentration is increased further the flame speed first increases, passes through a maximum, and then decreases until the flame is extinguished at a con- centration called the upper or rich limit. Above this upper limit, the

system is fuel rich and the oxygen concentration is too low to support

combustion. For our present purpose of defining conditions which can

lead to a flash fire we will be concerned only with the lower flammability limit since a fuel rich mixture can always pass into the flammable

region by the addition of air. Then for a flash fire to occur, we can

say that the fuel concentration must exceed the lower flammability limit

and materials which produce large quantities of gaseous fuels during

pyrolysis have a high flash fire potential.

The lower flammability limit varies only slightly with temperature and

pressure within the normal range of atmospheric conditions. Lower

limits have been measured for a variety of fuels [4]. The lower limit

for a mixture of fuels can be calculated from the individual values by

Le Chatelier's law.

100

LL = n

where c^ and LL_^ are the percentage composition and lower limit, respectively, of the ith combustible in the mixture. If we know the quantities

and species of fuel gases produced by the pyrolysis of a material we can calculate the lower limit and the quantity of material which will produce

flash fire conditions in a given volume of air. The mixtures of products

that are produced by the pyrolysis of most organic materials are, however, so complex that this procedure is quite difficult and therefore of

little practical value. Fortunately, a simplifying generalization makes

this complex analytical task unnecessary.

THE MINIMUM ENERGY PRINCIPLE

Lower flammability limits have been measured for a variety of organic

vapors [5]. The percentage of fuel by volume in the lower limit mixture

varies widely, but the product of lower limit fuel concentration per

5
unit volume and heat of combustion is nearly constant for most organic

fuels (table 6) [6] . A few highly unsaturated compounds and non-organic

species deviate significantly from this rule, but these are unlikely to

be important in our application. Then at the lower flammability limit we have

(x) TT * AH = 10.4 + 0.8 K cal mole of mixture or LL c —

425 + 33 cal L~ 1 at 25 °C, 760 mm

where (x)pp is the mole fraction of the fuel vapor in the lower limit

mixture and AH^ is the heat of combustion of the fuel. Obviously, if

(x) • AH > 10.4

c

the mixture is flammable while if

(x) AH < 10.4

c

the fuel-air mixture is below the flammable limit. From Le Chatelier's

Law, it follows that for a mixture of fuels at the lower limit

AH « 10.4

c i

where x. is the mole fraction of the ith fuel species, AH„ is its heat

i

L

i

of combustion, and the sum is taken over all fuel species present. When

the sum exceeds 10.4 the mixture is in the flammable range and a flash

fire is possible. Thus it is not necessary to know the detailed composition of a complex pyrolyzate mixture or the flammability limits of the

individual components in order to estimate its potential to produce a flash fire. It is only necessary to know the total heat of combustion

of the pyrolyzate/air mixture.

This minimum energy principle may be further rationalized if we note

that the flame temperature of a pre-mixed fuel air mixture is closely

related to the heat of combustion of the mixture. The concept of a minimum combustion energy necessary to support a flash fire is then

equivalent to a minimum flame temperature necessary to support a stable

combustion wave.

A variety of experiments were performed to investigate the applicability

of the minimum energy principle to the flash fire problem.

6
EXPERIMENTAL MATERIALS

Four flexible polyurethane foams typical of compositions used in seating

construction were selected for detailed study. Two of the foams con- tained fire retardants while two were unretarded. All were of the TDI - poly (propylene oxide) type made with a Sn-amine catalyst. Some of

their properties are given in table 7.

METHODS OF EXPERIMENTAL MEASUREMENT OF THE ENERGY CONTENT OF PYROLYSIS

GASES

Several methods of measuring the energy content of the pyrolysis gases

were investigated. The method of McCarter [7] has been used extensively

in this laboratory to study pyrolysis processes. In this method, the

pyrolysis gases, thermally cracked and mixed with air, are carried over

a heated catalytic surface. Oxidation of the fuel occurs on the catalyst

surface, raising its temperature. The temperature rise gives a measure

of the fuel concentration when the instrument is calibrated against

known amounts of fuel. The detector's response varies from compound to

compound, making it unsuitable for the precise measurement of the energy

content of unknown mixtures. Its response to aerosols and particulates

is also uncertain. The method is being studied further by Min [8] and a more useful procedure may result. Rather than thermally "crack" the

pyrolysis products prior to measurement with the catalytic detector, it was preferred to attempt a direct measurement in another type of detector.

The flame ionization detector, on the other hand, shows a more uniform

sensitivity toward organic compounds than the catalytic detector. However, it is insensitive to hydrogen and carbon monoxide and its response

to particulates is uncertain. In these studies it was used both as a modification of the McCarter pyrolysis technique and for the analysis of

grab samples from the flash fire cell, both with and without partial

chromatographic separation of fuel species.

Another possible technique has been described recently by Shafizadeh [9]

who measured the oxygen consumed in the combustion of pyrolysis products

from cellulose. It is well known that for most organic compounds the

energy release per unit mass of oxygen consumed is approximately a constant. This is another manifestation of the minimum energy principle

since, for a complex mixture of fuels, the energy available to drive the

combustion wave can be characterized more readily by the amount of

oxygen consumed than by properties of the fuel. The oxygen consumption

method may be useful in further studies of the flash fire problem.

7
MEASUREMENT OF ENERGY CONTENT OF PYROLYSIS GASES IN THE FLASH FIRE CELL

The most direct method of determining the energy content of the pyrolysis

gases appeared to be through the study of samples removed from the flash

fire cell. Experiments were carried out on the four polyurethanes described above by the procedure used for the determination of minimum

mass. Gas samples were withdrawn from the cell by means of a gas tight

syringe immediately before ignition and, in the case of a flash, after

ignition. The heat of combustion of the sample was determined by injecting it into a gas chromatograph with flame ionization detectors. The

detectors were calibrated with known quantities of methane, so the

energy content of the unknown gas mixture could be reported in methane

equivalence

.

A Varian Aerograph 200 series gas chromatograph with dual flame ionization detectors was used for these measurements. One side of the chromato

graph used an unpacked column for the methane equivalent measurements

while the other side contained a 6 -ft 0V-101 packed column. All analyses

were run isothermally at 60 °C. The OV-101 packed column permitted

separation of the lighter fuel components up to about C 5 while the empty

column passed the entire fuel mixture without separation. The syringe

sampling technique undoubtedly removed most of the particulate matter

from the sample.

In the case of a flash, the flame speed (S ) was also measured by measuring the times of arrival of the flame front at two thermocouples placed

25 cm apart. Because of the design of the apparatus, these measurements

do not represent true flame speeds, but they do allow useful comparisons

to be made. The flame speed for a lean methane-air mixture as measured

in the flash fire apparatus was found to be approximately 250 cm s -

. The reported flame speed of a lean methane-air mixture lies in the range

of 30-37 s

1 [10] . The results of these experiments are summarized in

tables 8 and 9. In table 8 , the mass of each sample is tabulated with

the oxygen concentration at the time of a flash [ 0

2

] , the maximum tempera

ture reached by the sample (T ) and the upward propagation speed of the

flame front (S ). Table 9 shows the sample mass, the amount of organic

combustible gas content prior to and after a flash in terms of equivalent

methane [CH4 ] and the energy content (AH) of these gases prior to a flash

.

The samples containing fire retardants (38 and 42) show significantly

higher minimum masses than the unretarded samples. The flame speeds appear to fall into two groups, 30 to 60 cm s and >100 cm s . We can speculate that at the higher flame speeds the fuel vapor concentration

was high enough to support the flame while at the lower speeds the

volatilization of a significant amount of fuel from the particulates is

necessary to provide a flammable mixture. It is known that flame propagation rates in mists and dust clouds are much lower than in homogeneous

gas mixtures with similar energy contents [11]. These preliminary

experimental results indicate that the flame speed approaches a lower

limiting value (30-40 cm s ) as the sample mass approaches its minimum

mass . 8
This view is supported by the results of the energy content measurements

reported in table 9. In most cases the energy content of the gas, as calculated from the flame ionization data where particulates were presumably eliminated, was below the minimum level necessary to propagate

a flame (10.4 k cal mole of mixture) even though the original mixture

containing particulates flashed in the flash fire cell. The presence

of significant fuel concentration in the cell after the passage of the

flame front also suggests that additional fuel is vaporizing from particulates not completely consumed in the flash fire.

Further improvements in the accuracy of the measurements will be needed

before a more detailed interpretation of these experiments can be made.

Reproducibility is a greater problem in these types of experiments

than precision. A lack of reproducibility leads to a lower accuracy.

PROBE PYROLYSIS EXPERIMENTS

In an effort to develop a simpler and more direct method of determining

the heat content of the pyrolysis gases, experiments were carried out by

pyrolyzing the samples in the inlet port of the gas chromatograph [7, 12].

A pyrolysis probe made by Chemical Data Systems was coupled to the inlet

port of a Varian gas chromatograph. The heating rate of the probe could

be set between 1 and 5 °C per second and the probe could be programmed to

maintain a pre-selected maximum temperature. A sample of between 0.1

and 0.3 mg of polyurethane was placed in a quartz capillary tube which

could be inserted into the platinum wire heating coil of the probe. The

samples were heated at a rate of 5 °C per second to a maximum temperature

of 560 °C. The pyrolysis was carried out in a stream of nitrogen. The

pyrolysis gases were carried through a heated blank column directly to

the flame ionization detector of the chromatograph. Probe temperature

and detector output were recorded simultaneously so the output of com- bustible gases could be observed as a function of temperature. Integration of the detector output and calibration with known quantities of

methane provided a measure of the total energy content of the pyrolysis

gases. Typical runs are shown in figures 3, 4, 5 and 6. The individual

samples are discussed below. The average value and standard deviation of

the energy content per unit mass of the pyrolysis products (AH pyrolyzate)

of each sample is listed in table 10.

SAMPLE 8

A pyrolysis run of sample 8 is shown in figure 3. There are two major

decompositions. The first occurs in the temperature range 190-370 °C

and the second 330-460 °C. The peak maxima occur at 292 0 and 402 °C.

The larger peak represents about 70% of the total amount of combustibles

evolved. The shape of the first peak indicates the summation of at least

two decomposition reactions and possibly more. The tail after the major

decomposition is thought to be due to further decomposition of the

residue. The dashed lines represent an attempt to separate the main

reactions

.

9
SAMPLE 16

A pyrolysis run of Sample 16 is shown in figure 4. Again there are two

major decompositions with the first decomposition occurring in the temperature range 185-345 °C. The peak maximum occurs near 278 °C. The

major decomposition peak, which contributes about 72% of the total

amount of the combustibles evolved, occurs in the temperature range

280—450 °C. The peak maximum occurs at 390 °C.

SAMPLE 38

A pyrolysis run of sample 38 is shown in figure 5. There are again two

temperature regions of decompositions. The first which appears to involve several decomposition reactions occurs in the temperature range

150-350 °C with the peak at about 267 °C. The major peak occurs in the

temperature range 290-455 °C with the peak maximum occurring near 400 °C.

The major peak represents about 66% of the total amount of combustibles

evolved

.

SAMPLE 42

A pyrolysis run of sample 42 is shown in figure 6. The two decompositions which occur are similar to the previous sample. The initial peak,

which appears to involve several reactions, occurs in the temperature

range 160-335 °C with the peak maximum occurring at 260 °C. The major

decomposition reaction occurs in the temperature range 280-455 ° C and

the peak maximum occurs at about 388 °C. The major decomposition represents about 65% of the total amount of combustibles evolved.

The pyrolysis patterns of the fire retarded and unretarded polyurethanes

are quite similar. The maximum of the major peak agrees with the previous result [2] that the minimum sample temperature for a flash to occur for polyurethane was 390 °C. The major peak constitutes about 70%

of the total amount of pyrolyzate evolved in each case and the amount

of combustibles produced per unit mass is similar, yet the minimum mass

of the retarded and unretarded polyurethane samples as determined in the

flash fire cell differs by about a factor of two. The flame retardant

treatment caused little change in decomposition temperatures or amounts

of flammable pyrolyzate. Effective condensed phase flame retardants

usually cause a decrease in pyrolysis temperature and reduce the quantity

of flammable pyrolysis products. This suggests that the fire retardant

is active in the vapor phase.

SUMMARY OF ENERGY CONTENT MEASUREMENTS

The results of the energy measurements are summarized in table 10. Heats

of combustion (AHC ) of the polyurethanes were determined in an oxygen

bomb calorimeter. Despite the scatter in the results, it is apparent

10
that the pyrolysis probe experiments gave values for the heat of com- bustion of the pyrolysis products (AH pyrolyzates) which approximate

those of the foam while the flash fire cell experiments give much lower

energy values (AH flash cell) . These results are not unexpected since

the pyrolysis experiments were conducted in nitrogen and the pyrolysis

products were introduced directly into the detector. Under these con- ditions, no oxidation would occur prior to introduction of the pyrolyzates into the detector and the only energy loss would be due to the

heat of pyrolysis of the sample, incomplete pyrolysis, and possible loss

of particulate matter in the short space from probe to detector. In the

flash fire cell, on the other hand, the pyrolysis is conducted in air and

considerable oxidation may occur in the process. The sampling method

also undoubtedly results in extensive loss of particulate matter.

These differences are demonstrated further in table 11 where the

available energy per unit volume of pyrolyzate mixture, as determined

at the minimum mass level by the various techniques, is compared with

the theoretical minimum energy level necessary to support a flash fire

(425 cal L *). The total energy theoretically available from the pyrolysis of the minimum mass of polyurethane is from 2.5 to 5 times as great

as that needed to support a flash fire. On the other hand, the measured

energy content of the vapor phase in the flash fire cell is somewhat less

than the amount needed to support combustion. The difference is due to

partial oxidation during pyrolysis and the formation of particulates in

the flash fire cell.

The pyrolysis probe experiments could be repeated in air to give an indication of the importance of oxidative processes during pyrolysis.

Experiments of the type described here can give a great deal of information on the pyrolysis properties of materials and the flammability of

the resulting product mixtures. Further refinements in experimental

technique are needed before more detailed conclusions can be drawn.

GAS ANALYSIS EXPERIMENTS

In an effort to learn more of the details of the pyrolysis process, the

light gases produced by the pyrolysis of the unretarded samples 8 and 16

in the flash fire cell were analyzed. Pyrolysis was carried out by the

standard procedure. Gas samples were withdrawn from the flash fire cell

and analyzed with a Carle AGC 311 gas chromatograph. A 6 ft molecular

sieve column and a thermal conductivity detector were used for the light

gas analysis. A flame ionization detector was also used for the hydrocarbon analysis. The results are summarized in table 12.

It is apparent that carbon monoxide (LL 12.5%) can make a significant

contribution to the flash fire potential of sample 8, particularly when

the pyrolysis is carried out at the higher temperatures. Sample 16, on

the other hand, produces much less CO. The change in the oxygen/nitrogen

ratio is a direct measure of the oxygen consumed during pyrolysis.

Oxygen consumption is significant for sample 8, particularly at the

11
higher temperature, but appears to be much less for sample 16. Since

comsumption of all of the oxygen in the flash fire cell would correspond

to an energy release of about 1500 cal, comparison with the values in

table 11 indicates that oxidative pyrolysis can have a significant effect

on the residual energy content of the pyrolysis gases.

SUMMARY AND CONCLUSIONS

A flash fire cell was developed to provide a method of evaluating the

relative flash fire potential of aircraft cabin interior materials.

Twenty four typical cabin materials were examined by this method. The

method is convenient and provides good discrimination between materials.

In applying the results to the development of safer aircraft interiors,

the quantity of material and the likelihood of its being exposed to fire

conditions should be considered along with its intrinsic flash fire

potential.

A minimum energy principle was proposed to characterize the flash fire

behavior of the complex mixture of fuels derived from the pyrolysis of

organic materials. This principle states that a flash fire is possible

when the potential combustion energy content of the pyroly zate-air

mixture exceeds approximately 425 cal L ^

.

A variety of experiments was performed to provide support for the

minimum energy principle. The results were in general agreement with

predictions, but the accuracy of the measurements was not good enough

to permit detailed conclusions.

Oxidative pyrolysis plays a significant role in the formation of the

fuel-air mixture in the flash fire cell. Particulates contribute to the

creation of flash fire conditions, but they present a difficult

measurement problem.

12
REFERENCES

[1] Paabo, M. and Comeford, J. J. , A Study of the Decomposition

Products of Polyurethane Foam Related to Aircraft Cabin Flash

Fires, National Bureau of Standards (U.S.) Report No. FAA-RD-73-46

(1973)

.

[2] Brown, J. E. and Comeford, J. J., Technique for the Measurement of

Flash Fire Potential of Polymeric Materials, National Bureau of

Standards (U.S.) Internal Report No. 75-757 (1975).

[3] Pagni, P. J. and Shih, T-M. , Excess Pyrolyzate, 16th Symposium

(International) on Combustion, 1976.

[4] Hertzberg, M., The Theory of Flammability Limits, Bureau of Mines

Report of Investigations 8127 (1976).

[5] Zabetakis, M. G., Flammability Characteristics of Combustible Gases

and Vapors, Bureau of Mines Bulletin 627 (1965).

[6] Kuchta, J. M. , Fire and Explosion Manual for Aircraft Accident

Investigators, Technical Report No. 4193, Bureau of Mines,

Pittsburgh, Pa. (1973).

[7] McCarter, R. J., J. Appl. Poly. Sci. , 17 1833 (1973).

[8] Min, K. , Dynamics of Pyrolysis of Cellulosis Materials, Paper

presented at the Central States Meeting of the Combustion

Institute, San Antonio, 1975.

[9] Shafizadeh, F., University of Montana. Private communication,

to be published.

[10] Coward, H. F. and Jones, G. W. , Limits of Flammability of

Gases and Vapors, U. S. Bureau of Mines Bulletin No. 503 (1952).

[11] Burgoyne, J. H. , The Flammability of Mists and Sprays, Second

Symposium on Chemical Process Hazards, p. 1 (1963).

[12] Eggertsen, F. T. and Stross, F. H. , Thermochim . Acta , 1 , 451

(1970).

[13] McCarter, R. J. , J. Cons. Prod. Flam. , 3^, 128 (1976).

13
Table 1. Materials Evaluated in Flash Fire Cell

Sample

1

2

6A

10

14

26

27

32

33

34

37

50

61

66

No . Material Description

Tedlar finish, epoxy-fiberglass faces

Nomex honeycomb core

Epoxy-fiberglass faces, Nomex honeycomb

core

Tedlar finish, PRD-49 Kevlar-phenolic

finish

Polyester-fiberglass sheet

Perforated Tedlar finish, Nomex

paper-epoxy front face, Nomex

honeycomb core, fiberglass-epoxy

back face

Epoxy-fiberglass sheet

Fiberglass batting, melamine binder

Molded Lexan polycarbonate

Wool pile, polyester backing and FR

latex back coating

Wool pile face, polyester backing, FR

latex back coating, urethane foam pad

and nylon scrim

Tedlar finish, fiberglass screen, Nomex

honeycomb core filled with fiberglass

batting, phenolic/ epoxy- f iberglass

back face

Wool carpet finish, phenolic/epoxyfiberglass front face, epoxy adhesive,

Nomex honeycomb, epoxy-fiberglass back

face

Tedlar/PVC finish, phenolic-fiberglass

front face, epoxy adhesive, Nomex

honeycomb core, phenolic-fiberglass

back face

Silicone treated, phenolic impregnated

fiberglass batt

Usage

Ceiling panel

Ceiling panel

Window reveals

and sidewalls

Cargo liner

Wall panel

Cargo liner

Cabin insulation

Access cover

Carpet

Carpet

Center ceiling

panel

Lower sidewall

panel

Overhead

stowage panel

Cabin insulation

14
Table 1 (continued)

Sample No. Material Description Usage

67 PVC finish, phenolic/epoxy-fiberglass

front face, epoxy adhesive, Nomex

honeycomb core, epoxy-fiberglass

back face

Door liner

78 Nomex fabric Attendant seat cover

86 PVC foam Flotation, seat

back and arm rest

padding

88 FR wool fabric Crew seat cover

111 Lexan polycarbonate sheet Transparency

115A Phenolic impregnated fiberglass batt Cabin insulation

117 Noryl poly (phenylene oxide) thermoforming material

Passenger service

unit

130 FR coating, cotton/rayon fabric Attendant seat cover

143A Polyester urethane foam Seat cushion

143C Polyester urethane foam Seat cushion

15
Table 2. Flash Fire Test Results

Sample Min. Mass, gL

1 >2.77

2 2.91

6A >1.41

10 0.84

14 4.30

26 >2.04

27 >1.83

32 1.20

33 0.55

34 0.55

37 >2.35

50 >1.70

61 <3.30

66 >2.35

67 >3.67

78 >2.09

86 0.67

88 0.62

111 1.25

115A >2.35

117 0.23

130 • >1.37

143A 0.41

143C 0.72

T

sample, C [O^l^vol. %

420-480 12-14

430-480 17-19

460-470 16-17

400-440 19-20

480-500 18-19

430-500 14-16

500 17.5

470-500 18-19

440-480 18-19

430-470 16-18

480-500 15-17

475-495 14-15

480-500 16-18

500 19

460-470 15-17

480-500 16

500-540 15-18

420-460 17-18

500 18-19

500 18

450-480 19-20

460 10

430-500 15-19

420-500 17-19

a Minimum mass for samples which flashed; largest sample tested for

those which did not flash.

b Maximum temperature reached by sample at time of flash or maximum

temperature reached in case of samples which did not flash.

c Oxygen concentration at time of flash or minimum concentration

reached in case where samples did not flash.

d Sample flashed. Shortage of material prevented testing smaller

samples

.

e Oven temperature 600 °C.

16
Table

3.

Ranking

of

FAA

Samples

which

Flashed

Table

4.

FAA

Samples

which

Failed

to

Produce

Flash

under

the

Test

Conditions

cd

i hJM

<U

cn

0) H

rH o CO <3- CTn m in r*^

0) ro 00 o o CO cn CO r^* c£> rH • a i—

i

r—

1

i—

H

rH CN CN CN CN CN CN CO e

cd coe

3

E

•HX

cd ST

CN co oo r-^ cocn r-~ cn vo <

LO 1"- \D

I hJ

OC

COM

cd S

co rH m in CN CN o n i—

1

o o

CN m m CO cO 00 CN CN ON co CO o o o o o o o o rH H CN COv

3

•Hs

<u —

i

a

E

cd co

<cn cn

<r cn

CJ <r oo vo cn cd cn cn oo oo oo

CN i—I vf

CO rH

c

cd Pi

cn cn n co r-^ oo on cn

17

i
Table 5. Results of Composite Samples

Sample Component Weight Fraction gL‘

1 Epoxy Fiberglas (A) 0.47 >3.48

Epoxy Fiberglas (B) 0.30 >3.83

Nomex Core 0.23

2 Epoxy Fiberglas (A) 0.39 2.77

Epoxy Fiberglas (B) 0.37 <3.79

Nomex Core 0.24

14 Nomex-Epoxy (A) 0.43 1.31

Epoxy-Fiberglas (B) 0.11 >3.92

Nomex Core 0.46

37 Fiberglas (A) 0. 25

Nomex-Fiberglas Core 0.41

Pehno lie /Epoxy-Fiberglas (B) 0.34 >3.09

50 Wool 0. 30 >1.53

Nomex Epoxy Fiberglas 0.70

61 Phenolic Fiberglas (A) 0.39 <3.96

Phenolic Fiberglas (B) 0.32 <3.96

Nomex Core 0. 28

67 Phenolic Epoxy Fiberglas (A) 0. 76 >3.96

Epoxy-Fiberglas (B) 0.14 >3.96

Nomex core 0.10

Minimum Mass,

1

>2.87

A — front face

B — back face

18
Table 6. Lean Limit Mixture Heats of Combustion for

Upward Flame Propagation of Organic Fuels

Fuel (x) LL , Vol . % AH , kcal'mole * c ^LL . AH

100

Methane 5.00 191.76 9.6

Ethane 2.95 341.26 10.

1

Propane 2.12 488.53 10.4

n-Pentane 1.41 782.04 10.9

cyclo-Hexane 1.3 908 11.8

Propylene 2.0 460.4 9.2

Benzene 1.3 757.5 9.8

Toluene 1.2 901.5 10.8

Pyridine 1.8 633 11.4

Ethanol 3.3 306 10.

1

Ethylene glycol 3.2 311 10. 0

Methyl ether 3.4 316 10.7

Acetone 2.6 403 10.5

Acetaldehyde 4.0 264 10. 6

Ethyl acetate 2.2 504 11.1

Average * 10.4

Data taken from

± 0.8

reference 6.

(c) Table 7. Properties of Polyurethane Foam Samples

Sample

No.

Polyol Flame

Retardant

Density

kg/m 3 n

(b) Oxygen

Index

8 ungrafted none 29 15 1/2

16 graf ted none 40 20 1/2

38 ungrafted Br,P 35 21

42 grafted Br,P 72 29

(a) Polyacrylonitrile grafted to the polyol

(b) per ASTM D 2863-70

(c) Data from reference 13

19
Table 8. Results of Flash Fire Experiments for Samples 8, 16, 38 & 42

3. b Sample Mass, [O 2 ], T s , Flash? S u , g vol. % °C cm sec

0.4228 18.7 467 YES 125

0.3801 18.6 500 YES 56

0.3415 18.3 483 YES 143

0.3410 18.7 466 YES 30

0. 3383 17.1 452 YES 222

0.3240 19.0 500 YES 37

0.3045 15.7 468 NO —

0.4813 16.7 393 YES 42

0.4151 15.1 438 YES 167

0.4130 14.6 . 435 YES 56

'Trr^r030 16.9 359 YES 36

0.3664 15.6 345 NO —

0.3052 15.7 345 NO —

0.6827 17.2 427 YES 31

0.6611 17.6 433 YES

0. 6570 17.3 399 YES 34

0.6454 16.2 427 NO —

0.6308 14.2 374 NO —

0.6780 16.6 445 YES

0.6712 16.2 445 YES 36

0.6488 17.4 433 NO —

0. 6270 16.6 414 NO —

0.6209 15.9 362 YES 42

0.6033 13.7 386 NO —

0.5795 16.3 340 NO —

0.5363 15.1 360 NO —

0.5026 14.9 354 NO —

0.4375 16.2 377 NO —

Oxygen concentration at flash or minimum oxygen concentration

reached in case where sample did not flash.

Maximum temperature reached by sample.

20
Table 9. Results of Energy Measurements of Flash Fire

Experiments for Samples 8, 16, 38 and 42

Sample Mass

,

g

Flash [ch4 ] vol%

[ch 4 1 vol%

AH/100

k cal mo

8 Q. 3415 YES 3.0 1.1 5.8

2.2 1.4 4.2

0.3383 YES 2.9 0. 7 5.6

3.6 0.7 6.9

0.3443 YES 4.1 0. 5 7.9

3.8 0.2 7.3

16 0.4130 YES 4.1 1.1 7.9

0.4151 YES 3.6 0.3 6.9

4.3 0.6 8.3

38 0.6611 YES 2.1 1.0 4.0

0. 6826 YES 3.2 0.4 6.1

0. 5 0. 6827 YES 3.0 0. 5 5.8

0. 9

42 0. 6270 NO 3.6 6.9

0.6488 NO 1.8 3.5

0.6712 YES 3.9 2.4 7.5

2.8 2.1 5.4

0.6780 YES 6.6 2.0 12.7

8.6 1.8 16.5

Methane equivalent before flash

Methane equivalent after flash

21
Table

10.

Energy

Measurements

from

Flash

Fire

Experiments t

00 rH

QJ i—

H 1—1

CJI

CO kJ

CJ CN On PP cn co CN CO rH * CN pH cn rH CO CO

r-H i—1 CJ i—1

+1 +1 +1 

+1 MH

0) PC a o CN ON <a CN cn rH <r

pc VO

m

O vD

CO rH

H

pc<3

00

PC<

CON

to rHou

Oo

Q.

O0

PC<

COe

CO CO

m o 00 nCN rH nO H o cn rv£) vO m m

00 NO oo

cn

CNI Of

•HC 0) •H H 2 CO rH N 1 CD CO Jo H o <r CN

PO T3 r—l 00 rH rH

-M

O

O rH ON v£> a>

PC >H CO

H *H

•U 4-1 >N

O

CO CD

a S PC

0) <c E co 3 3

r-l

O

O -H CN CN > u O CN O 00 CO o cn rH m 4J >

tH iH rH tH •HC Oo

HI HI +1 HI P0 PP <r vD cn t-i TO CO rH VO rH in a) a) CO iH On rH CL c CO m m •H s

Oo

00

l-l a)

cc w

40 CO O CO C -W O -H

CO E

*H *H

tH rJ

cOCL CO g co O CO o 2 c

•Hr

PC< # CO tH CO

m 00

rH CO tH CO 00

T- r-l ON cn 00

<U 1 i—1 CN cn

r-H . hJ • • . x> c 00 o o o

*H

H saE

cO co

rH nO

rH NO

cn cn

cn

onco

inmino

in

CNI <r

CNI

CNI

nO 00

CO

CNI

22

0.3674

2100

1893

238
Gas

Analysis

Results

from

Flash

Fire

Cell

Experiments

OJ

CO H

•rH <—i \

C\J ON vO CN *<r UO t-H

C\l <£) vO vO 00 On O • • • • • • • • • '•w'

CN

CN o i—i

<r UO UO UO 00 ON r^

CN 00 CO CN <r vD o o co

2T vD \D vO vD vD uo o CO <T CO \D UO CN o T) • • • • • • • • • CN UO CN CN o UO UO 'O' o rH rH t-H t-H t-H rH t-H rH t-H

0/e ON CN 00 o t-H o 3 —1 • • • • • • • • • rH CN CN CN o O CN \D CO o c rH t-H rH t-H rH t—i

t-H rH i—

H >xc CM co CO o O a> UO o -4 o o rH CN CN o O o O

•H

X • • • • • • • • • 4J u o o o o O o O o o

tou

4-1 c 01

01 -H

u CN UO UO UO CO 00 uo

J 4- CTJ o o t-H t—H o o o o c 30 H • • • • • • • • o U 4-J o o o o o o o o ax

cO o t-H rH CN 00 ON co 00 • • • • • • a o o rH CN co O o rH o

CSJ CO UO o CN UO rH CN o O • • • • • • • U o o t-H rH CN t-H t-H H rH u 33

0) o OJ 33

t-H CO 0) a 3 X E 01 33 3

CO S-i

U 0/ cn 3 O X S-i 4J uO UO o t-H UO co 00 4-1 3 o E 3 CN CO v£> On o- CJ 4-1 3 U CO co CO CO co co CO <r 01 U CJ E QJ 0 a; •H a 0) 4-1 4J X E 33 U 0)

CO 01 a/ 33 s H >. 4-> 4J 0) a

•h -a *H > X

•H

C

a

oo •u

O 3 O *H >-4 * UO CN ON U0 H co t-H UO 3 4J 00 X o CO o vO ON On o> 33 3 >H X <r <r CO CO CO co CO co C N 3 3 • • • • • • • • • 0 -H t-H S O o o o o o o o o U C o o a

rH *H 3 c £ 0) a) 3 S- £ 00

r—1

<3 3 a 00 X >-h

X E t-H H X o 3

C/0 rH CNi

m

23
FIGURE 1. MODIFIED FLASH FIRE CELL

24
21

20

19

18

17

16

15

14

13

12

T SAMPLE

J L

1 2

J L 3 4 5 Time, Min.

500°

400°

- 300°

200°

100°

FIGURE 2. TYPICAL EXPERIMENTAL RUN WHERE SAMPLE

PYROLYZATES PRODUCE A FLASH FIRE

25

SAMPLE,

°C
SAMPLE

8

'dSNOdsau Hoioaiao

26

FIGURE

3.

PYROGRAM

OF

SAMPLE

8

IN

NITROGEN
SAMPLE

16

3SNOdS36 60133130

27

FIGURE

4.

PYROGRAM

OF

SAMPLE

16

IN

NITROGEN
I

BSNOdSBH HOlOBiBQ

28

FIGURE

5.

PYROGRAM

OF

SAMPLE

38

IN

NITROGEN
SAMPLE

42

3SNOdS3H H013313Q

29

FIGURE

6.

PYROGRAM

OF

SAMPLE

42

IN

NITROGEN