DOT/FAA/AR-05/14 

Office of Aviation Research 

Washington, D.C. 20591

Polymer Flammability 

May 2005 

Final Report 

This document is available to the U.S. public 

through the National Technical Information 

Service (NTIS), Springfield, Virginia 22161. 

U.S. Department of Transportation 

Federal Aviation Administration
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 Technical Report Documentation Page

1. Report No.

DOT/FAA/AR-05/14

2. Government Accession No. 3. Recipient's Catalog No.

5. Report Date 

May 2005

 4. Title and Subtitle 

POLYMER FLAMMABILITY 6. Performing Organization Code

7. Author(s)

Richard E. Lyon and Marc L. Janssens* 

8. Performing Organization Report No. 

10. Work Unit No. (TRAIS) 

 

9. Performing Organization Name and Address

*Southwest Research Institute 

6220 Culebra Rd. 

P.O. Drawer 28510 

San Antonio, TX 78228-0510

11. Contract or Grant No.

 

13. Type of Report and Period Covered

 Final Report

12. Sponsoring Agency Name and Address

U.S. Department of Transportation 

Federal Aviation Administration

Office of Aviation Research 

Washington, DC 20591

14. Sponsoring Agency Code

 ANM-110

15. Supplementary Notes 

16. Abstract 

This report provides an overview of polymer flammability from a materials science perspective and describes currently accepted 

test methods to quantify burning behavior. Simplifying assumptions about the gas and condensed phase processes of flaming 

combustion provide mathematical relationships between polymer properties, chemical structure, flame resistance, and fire 

behavior that can be used to design fire-resistant plastics. 

17. Key Words 

Polymer, Plastic, Flammability, Heat release rate, Flame, Fire, 

Combustion 

18. Distribution Statement 

This document is available to the public through the National 

Technical Information Service (NTIS) Springfield, Virginia 

22161.

19. Security Classif. (of this report) 

 Unclassified

20. Security Classif. (of this page) 

 Unclassified

21. No. of Pages 

 82 

22. Price

Form DOT F1700.7 (8-72) Reproduction of completed page authorized
ACKNOWLEDGEMENTS 

This work is dedicated to the memory of Dr. Thor I. Eklund, former FAA Branch Manager for 

Fire Research, whose vision and efforts made this report possible. 

iii/iv
TABLE OF CONTENTS 

Page 

EXECUTIVE SUMMARY xiii 

1. INTRODUCTION 1 

2. THE BURNING PROCESS 2 

2.1 The Gas Phase 3 

2.1.1 Kinetics 3 

2.1.2 Thermochemistry 5 

2.1.3 Energetics 6 

2.2 The Mesophase 7 

2.2.1 Kinetics 9 

2.2.2 Thermochemistry 12 

2.2.3 Energetics 14 

2.3 The Condensed Phase 15 

3. FIRE BEHAVIOR OF SOLID POLYMERS 17 

3.1 Ignition 17 

3.1.1 Chemical Criteria 18 

3.1.2 Thermal Criterion 20 

3.2 Steady Burning 22 

3.3 Unsteady Burning 24 

4. CHEMICAL STRUCTURE AND FIRE PROPERTIES 27 

4.1 Heat Transport 28 

4.2 Heat of Combustion 28 

4.3 Enthalpy of Gasification 29 

4.4 Ignition Temperature 30 

4.5 Char Yield 34 

4.6 Heat Release Rate 35 

4.7 Flame Resistance 38 

4.8 Smoke 40 

5. FIRE AND FLAMMABILITY TESTS 42 

v
5.1 Terminology: Fire Versus Flammability 42 

5.2 Fire and Flammability Test Applications 43 

5.2.1 Regulatory Compliance 43 

5.2.2 Quality Assurance and Research 43 

5.2.3 Data for Fire Safety Engineering Design and Analysis 43 

5.3 Fire and Flammability Test Standards 44 

5.3.1 Consensus-Based Test Standards 44 

5.3.2 Other Types of Test Standards 45 

5.4 Testing for Regulatory Compliance 45 

5.4.1 Typical Example of a Flammability Test 46 

5.4.2 Typical Examples of Fire Tests 47 

5.5 Testing for Quality Assurance and Research 50 

5.5.1 The LOI Test 50 

5.5.2 The Pyrolysis Combustion Flow Calorimeter 51 

5.6 Testing to Obtain Engineering Data 51 

5.6.1 Bench-Scale Calorimeters 51 

5.6.2 Large-Scale Calorimeters 54 

6. REFERENCES 56 

APPENDIX A—TABULAR DATA FOR POLYMERS

vi
LIST OF FIGURES 

Figure Page 

1 Heat Release Capacity, Cost, and Flame Resistance of Commercial Polymers 1 

2 Physical and Chemical Processes in the Flaming Combustion of Polymers 3 

3 Gas Phase Kinetics: Accelerating (f > g) , Steady Growth (f = g), and SteadyState (f < g) Radical Concentration Histories at Ignition 5 

4 Mesophase Profiles of Temperature, Viscosity, and Density During Flaming 

Combustion 8 

5 Phenomenology of Polymer Burning 8 

6 Fractional Mass Loss Rate Versus Temperature for Polybenzimidazole in TGA 

(β = 10 K/min) 9 

7 Char Mass Fraction in Fire Versus Anaerobic Pyrolysis 11 

8 Thermogravimetric Analysis Data for PMMA and PAI (a) Residual Mass Fraction 

Versus Temperature and (b) Mass Loss Rate Versus Temperature 13 

9 Char Mass Fraction Versus Hydrogen Mole Fraction in Polymer 14 

10 Temperature Dependence of Polymer Heat Capacity, Thermal Conductivity, 

and Density 16 

11 Ignition Temperature Versus External Heat Flux for PPS, PC, PA6, PBT, PS, PP, 

UPT, and PMMA 21 

12 Critical Heat Flux Versus Ignition Temperature 22 

13 Representative HRR Histories in Flaming Combustion for Thick and Thin 

Samples of Charring and Noncharring Polymers 23 

14 Average HRR in Flaming Combustion Versus Char Yield of Polymers 24 

15 Heat Release Rate Versus External Heat Flux Data for PA6 From Different 

Sources 25 

16 Ignition/Fire Point Temperature Versus Decomposition/Flash Point Temperature 

for Solid and Liquid Fuels 32 

17 Pyrolysis Temperature Versus Activation Energy of Polymers 33 

18 Average HRR Versus Heat Release Capacity of Polymers 36 

vii
19 Polymer Heat Release Capacities: Calculated Versus Measured Values 38 

20 Flammability Rating in UL 94 Test Versus Heat Release Capacity of 50 Polymers 39 

21 Limiting Oxygen Index Versus Heat Release Capacity for 50 Polymers 40 

22 Smoke Extinction Area Versus Flaming Combustion Efficiency (χ) for 40 

Polymers 41 

23 UL 94 Cabinet 46 

24 The Steiner Tunnel Test Apparatus 47 

25 The Radiant Flooring Panel Test Apparatus 48 

26 Rate of Heat Release Apparatus 49 

27 The LOI Test Apparatus 50 

28 Commercial Version of the Cone Calorimeter 52 

29 Commercial Version of the Fire Propagation Apparatus 53 

30 ISO 9705 Room/Corner Test in Progress 55 

viii
LIST OF TABLES 

Table Page 

1 Components of the Enthalpy of Gasification for PMMA, PS, and PE 15 

2 Mass Loss Rate, Effective HOC, and HRR at Ignition (Flash Point) and Incipient 

Burning/Extinction (Fire Point) 18 

3 Heats of Gasification, Pyrolysis Activation Energy, Char Yield, as Well as 

Calculated and Measured Molecular Weights of Decomposition Products for 

Some Polymers. 30 

4 Thermokinetic Properties of PMMA, PE, and Phenolic Triazine 31 

5 Group Contributions to the Decomposition Temperature of Polybenzimidazole 34 

6 Group Contributions to the Char Yield of Bisphenol-A Polycarbonate 35 

7 Group Contributions to the Heat Release Capacity of PET 38 

8 UL 94 20-mm Vertical Burning Test Classification Criteria 39 

ix
LIST OF ACRONYMS 

ABS Acrylonitrile-butadiene-styrene terpolymer 

C/H Carbon/hydrogen 

CFR Code of Federal Regulations 

CHF Critical heat flux 

EP Epoxy 

FSI Flame spread index 

H Horizontal test 

HOC Heat of combustion 

HRP Heat release parameter 

HRR Heat release rate 

ICAL Intermediate-Scale Calorimeter 

IEC International Electrotechnical Committee 

ISO International Organization for Standardization 

LFL Lower flammability limit 

LOI Limiting oxygen index 

MMA Methylmethacrylate 

MW Megawatt 

NBS National Bureau of Standards 

NFPA National Fire Protection Association 

PA polyamides 

PA6 Polycaprolactam 

PAI Polyamideimide 

PBI 2,2′-m-phenylene-5,5′-bibenzimidazole 

PBT Polybutylene-terephthalate 

PC Polycarbonate 

PCFC Pyrolysis combustion flow calorimeter 

PE Polyethylene 

PEEK Polyetheretherketone 

PEI Polyetherimide 

PES Polyethersufone 

PET Polyethyleneterephthalate 

PMMA Polymethylmethacrylate 

POM Polyoxymethylene 

PP Polypropylene 

PPO Polyphenyleneoxide 

PPS Polyphenylenesulfide 

PS Polystyrene 

PSU Polysufone 

PVC Polyvinylchloride 

RMD Reactive molecular dynamics 

SDI Smoke-developed index 

SEA Smoke extinction area 

TGA Thermogravimetric analyzer 

Tign Ignition temperature 

x
tign Time to ignition 

TRP Thermal response parameter 

UL Underwriters Laboratory 

UPT Unsaturated polyester thermoset resin 

V Vertical test 

VE Vinyl Ester 

xi/xii
EXECUTIVE SUMMARY

This report provides an overview of polymer flammability from a materials science perspective 

and describes currently accepted test methods to quantify burning behavior. Simplifying 

assumptions about the gas and condensed phase processes of flaming combustion provide 

mathematical relationships between polymer properties, chemical structure, flame resistance, and 

fire behavior that can be used to design fire-resistant plastics. 

xiii/xiv
1. INTRODUCTION. 

Plastics (polymers) are a large and growing fraction of the fire load in homes, commercial 

environments, and transportation [1-5]. Moreover, the plastics that are most widely used are the 

least expensive and tend to be the most flammable. Flammability, which generally refers to the 

propensity of a substance to ignite easily and burn rapidly with a flame, is one indicator of fire 

hazard. Figure 1 shows the relationship between two measures of flammability: heat release 

capacity (section 4.6) and flame resistance (section 5.4) versus the truckload price of commercial 

polymers. Flammability and cost span over two orders of magnitude. The commodity polymers 

costing less than about $1/pound comprise over 95% of the polymers in use, and these will 

continue to burn after brief exposure to a small flame. Engineering and specialty plastics costing 

over $2/pound are typically polymers with aromatic backbones and fluoropolymers, which selfextinguish or resist ignition because of high thermal stability or low fuel value. Figure 1 shows 

that the flame resistance of polymers does not always correlate with cost but does correlate 

reasonably well with heat release capacity. 

10

100

1,000

3,000

0.1 1 10 100 1,000

Self 

Sustained 

Burning

Self 

Extinguishing 

No Ignition

Commodity 

Polymers

Specialty 

Polymers

Engineering 

Polymers

Bulk Price ($/lb) 

Heat Release Capacity, 

ηc (J/g-K) 

10,000

FLAME RESISTANCE

Halogen containing

300

30

FIGURE 1. HEAT RELEASE CAPACITY, COST, AND FLAME RESISTANCE OF 

COMMERCIAL POLYMERS 

Regulations [1 and 5] governing the flammability of plastics (e.g., section 5.4) used in consumer 

electronics, electrical equipment, building and construction, home furnishings, automobiles, and 

public transportation have created an annual worldwide market of tens of billions of pounds for 

flame-retardant plastics [1]. The designations flame-retardant, flame resistant, or ignition 

resistant as it applies to these plastics typically refer to the tendency of a thin (2- to 3-mm) strip 

of the material to withstand a brief exposure to a Bunsen burner flame or a hot wire without 

continuing to burn. Flame or ignition resistance is a low level of fire safety that is intrinsic to 

heat-resistant polymers but can be achieved with commodity polymers by adding flame-retardant 

chemicals [1-4]. The economic incentive to add flame-retardants to commodity polymers to pass 

flammability requirements (i.e., the slope in figure 1) has focused polymer flammability research 

1
over the past few decades on the mechanisms and efficacy of flame-retardant additives [6-10], 

rather than on polymer flammability as an intrinsic material property. This trend in research, 

combined with the fact that flaming combustion of solids is a highly coupled, multiphased 

process and that fire test results depend on the apparatus, test conditions, and sample geometry, 

has limited the understanding of polymer flammability to a descriptive and qualitative nature. 

In this report, simplifying assumptions were made about the burning processes under welldefined (standardized) conditions to provide mathematical relationships between polymer 

chemical structure and flammability properties. Experimental data was used in lieu of, and in 

support of, analytic results drawn from the broad subject material that is listed in the references. 

The goal of this report was to provide a consistent, mechanistic interpretation of the burning 

process as it relates to synthetic polymers and to describe currently accepted test methods to 

quantify burning behavior. 

2. THE BURNING PROCESS. 

Gases and volatile liquids are small molecules that are held together by weak (< 1 kJ/kg) 

secondary chemical bonds. These volatile compounds spontaneously form combustible mixtures 

with air that ignite easily and burn with a high velocity. Polymers are very large (macro) 

molecules with the same intermolecular and intramolecular forces as low molecular weight 

compounds, but their boiling temperature is essentially infinite because of their high molecular 

weight. Consequently, both intermolecular and intramolecular (backbone) chemical bonds of 

polymers must be broken to generate volatile fuel species. This process requires a large (≈ 2 

MJ/kg) and continuous supply of thermal energy for ignition and sustained burning. 

Flaming combustion can be roughly divided into physical and chemical processes taking place in 

each of three separate phases: gas, mesophase, and condensed (liquid/solid) phase [6,7, and 10-

16]. The mesophase is the interface between the gas and condensed phase during burning. 

Figure 2 shows a schematic diagram of a horizontal polymer slab that is burning with a diffusion 

flame. The physical processes are shown on the left-hand side of figure 2, which include (1) 

energy transport by radiation and convection between the gas phase (flame) and the mesophase 

and (2) energy loss from the mesophase by mass transfer (vaporization of the pyrolysis gases) 

and conduction into the solid. At typical burning rates, the polymer surface (mesophase) recedes 

at a velocity of about 10-6 m/s. Conservation of momentum at the gas-mesophase boundary 

shows that fuel gases evolve at a relatively low velocity (≈ 10−3 m/s) compared to the burning 

velocity of these gases when mixed with air (≈ 1 m/s). Consequently, fuel generation is the ratelimiting step in polymer flaming combustion, and it is governed primarily by the rate at which 

heat and mass are transported to and from the polymer, respectively. 

The important chemical processes are shown on the right-hand side of figure 2, which include 

(1) thermal degradation of the polymer in a thin surface layer (the mesophase) as a consequence 

of the physical (energy transport) processes, (2) mixing of the volatile pyrolysis products with air 

by diffusion, and (3) combustion of the fuel-air mixture in a combustion zone that produces 

radiant energy over a spectrum of wavelengths including visible. The combustion zone is 

bounded by a fuel-rich region on the inside and a fuel-lean region on the outside. Increasing the 

concentration of oxygen in the environment is known to increase the flame heat flux, either due 

2
to a higher flame temperature, an increase in the volume of the combustion zone, or an increase 

in the soot concentration (luminosity) of the flame. The chemical and physical processes of 

flaming combustion particular to each of the gas, meso, and solid phases are treated separately 

below. 

POLYMER

Fuel Rich Limit

Fuel Lean Limit

AIR

COMBUSTION ZONE (Fuel/Air Mixture)

PHYSICAL CHEMICAL

Surface 

Reradiation

Conduction 

Flame 

Radiation

Far Field 

Radiation

Flame 

Convection Vaporization

Gas Phase

Mesophase

Condensed Phase

FUEL

Pyrolysis, Charring

Devitrification 

and Melting

FIGURE 2. PHYSICAL AND CHEMICAL PROCESSES IN THE FLAMING COMBUSTION 

OF POLYMERS 

2.1 THE GAS PHASE. 

2.1.1 Kinetics. 

Condensed phases (solids and liquids) of combustible compounds will only burn if they can be 

made to generate a volatile fuel and air mixture; therefore, the phenomena that led to ignition and 

the release of heat are those of the gas phase [11-19]. Although there are hundreds or thousands 

of chemical reactions going on in the flame that convert oxygen and fuel to stable combustion 

products, kinetic modeling and experimental data have shown that the burning velocity is most 

sensitive to the following reactions involving active radicals (denoted by •) of fuel (R), hydroxyl 

(OH), hydrogen (H), and oxygen (O), and halogen or phosphorus (X) are 

 RH →

k1

 R• + •H Initiation (1) 

•H + O2 →

k2

•OH + •O Branching 

•OH + CO →

k3

 CO2 + •H Propagation (and primary heat-producing reaction) 

3
•OH + H2 →

k4

 H2O + •H Propagation 

•H + O2 →

k5

•HO2 Termination 

•H + HX →

k6

 H2 + •X Inhibition 

•OH + HX →

k7

 H2O + •X Inhibition 

The set of seven radical reactions in equation 1 accounts for the key processes of initiation, 

branching, propagation, and termination typical of hydrocarbon fuels as well as the inhibition 

reactions that are important for polymers containing halogen or phosphorus in a low oxidation 

state. Because the concentrations of radicals are empirically related as [H] ≈ [OH] ≈ 2[O], the 

set of equations can be solved for the total concentration of active radicals: [n] = [H] + [O] + 

[OH]. Defining a rate of chain initiation, θ = k1[RH], a branching coefficient f = 2/5 k2[O2], and 

a linear termination coefficient, g = 2/5{k5[O2] + (k6+k7)[HX]}, the rate of change of radical 

concentration at time, t, is 

d[n]

dt

= θ+ f[n] − g[n] (2) 

The general solution of equation 2 for the total radical concentration at any time is 

[n] = θ

g − f

1 − e−(g− f) t ( ) (3) 

Figure 3 shows a plot of equation 3 for three special cases: 

• f > g: In this case, the branching reactions dominate and the radical concentration 

increases exponentially as [n] = (θ exp[(f-g)t]-1)/(f-g), until the reactants are depleted. 

• g = f: In this case, the radical concentration increases steadily with time as [n] = θ t, 

which is the boundary between steady state and exponential growth. 

• g > f: In this case, the rate of chain termination is greater than branching, and a steadystate concentration is reached at [n] = θ/(g-f). This steady state may be above or below 

the concentration for flame propagation. 

The molar inhibition efficiency of the halogen atoms X = bromine (Br), chlorine (Cl), and 

fluorine (F) is found to be in the ratio Br/Cl/F = 10/2/1, i.e., bromine is ten times more efficient 

than fluorine and five times more efficient than chlorine on a mole basis. On a mass basis, the 

inhibitor efficiency is Br/Cl/F = 2/1/1, which explains the widespread use of bromine-containing 

monomers and additives as flame-retardants [4-10]. 

4
Time

f > g

f < g

f = g

Effect of 

reactant 

consumption

0

Radical Concentration [n]

Steady Burning

FIGURE 3. GAS PHASE KINETICS: ACCELERATING (f > g), STEADY GROWTH (f = g), 

AND STEADY-STATE (f < g) RADICAL CONCENTRATION HISTORIES AT IGNITION 

2.1.2 Thermochemistry. 

If the kinetics are such that the combustion reactions proceed to completion at a rate that sustains 

flaming combustion, the chemical reaction of a generic fuel with atmospheric oxygen yields 

carbon dioxide (CO2), water (H2O), nitrogen (N2), and mineral acid (HX) in quantitative yield: 

 CcHhOmNnXx + (c + h − x − 2m

4 ) O2 → c CO2 + 

h − x

2

H20 + n

2

N2 + x HX (4) 

Equation 4 assumes complete, 100% efficient, conversion of reactants (fuel gases and O2) to 

products (CO2 and H2O). Flaming combustion efficiency rarely exceeds 99% and typically 

ranges from 50% to 95%. Smoke is a combination of complete (CO2, H2O, and acid gases) and 

incomplete (soot, carbon monoxide, and partially oxidized fuel gases) combustion products that 

occurs when combustion inhibitors are present, oxygen concentration is low, or there is 

insufficient reaction time or temperature in the combustion zone. The composition of smoke is 

highly dependent on the chemical composition of the polymer and the ventilation conditions 

under which the polymer is burning. Acid gases are irritating to the eyes and nasal passages, 

which makes escape more difficult. Carbon monoxide is the primary toxic compound in smoke. 

Soot absorbs light, which limits visibility and increases the luminosity or radiant power of the 

fire. Smoke is considered to be the main fire hazard but it depends on ventilation and the 

burning rate of the polymer; therefore, it is the latter quantity, i.e., the burning or heat release rate 

(HRR), that is considered to be the primary indicator of a fire hazard [4, 11, 12, 20, and 21]. 

The chemical pathway to soot formation is a recombination of aromatic radical fragments in the 

fuel-rich region inside the flame (see figure 2). Minute (10-100 nm in diameter) polycyclic, 

aromatic hydrocarbon particles are formed. These elementary soot particles may oxidize in the 

combustion zone of the flame. However, the elementary soot particles will agglomerate and 

grow in size until they are large enough to interact with visible light (0.3-0.7 μm), ultimately 

5
reaching sizes on the order of a micron that absorb infrared radiation. Smoke is a combination of 

these soot particles in an aerosol with unburned liquid hydrocarbons, carbon dioxide/monoxide, 

water, and halogen acid gases, if present in the burning polymer [11-13]. 

2.1.3 Energetics. 

Regardless of the gas phase combustion kinetics and thermochemistry, burning will only be 

possible if the energy balance is favorable. The first law of thermodynamics for a constant 

pressure gas phase process in which all of the work is pressure-volume work states that the 

internal energy change, dU, is related to the change in heat content, dQ. 

dU + PdV = dQ (5) 

If the volatile fuel and air are well-mixed and react to generate a power density Q (heat of 

combustion per unit volume per unit time, W/m

′′′ &

3

), a portion of which accumulates in the reaction 

volume as a rise in the temperature of the fuel-air mixture and a portion of which is lost to the 

surroundings at ambient temperature, Ta, by convection and radiation, the first law energy 

balance for the fuel-air mixture during deflagration (burning) is 

)TT( V

S )TT( VSh Q VdV P

dt

dT

c 4

a

4

a − εσ

=+ρ ′′′ −−− & (6) 

where ρ, c, V, and T are the instantaneous density, heat capacity, volume, and temperature of the 

fuel/combustion products/air mixture, h is the average heat transfer coefficient at the boundary 

between the combustible mixture and the environment having surface area, S, at temperature, T, 

and pressure, P. In equation 6, ε is the gas emissivity and σ is the Stefan-Boltzmann constant. 

Defining quantities: θ = T − Ta, τ = ρcV/ h S, and assuming a constant fraction, φ, of the power 

density is lost by radiation to the surroundings. 

Q)TT( V

S 4

a

4 φ≈−εσ ′′′ & (7) 

Substituting equation 7 into equation 6, rearranging, and separating variables 

[ φ)(1Q dlnVP ]

ρc

1

τ

θ

dt

dθ =− ′′′ −− & (8) 

where , ρ, and c are initial values for the mixture. If deflagration (burning) raises the 

temperature from T

Q ′′′ &

a to Tf with a corresponding increase in volume from Va to Vf at constant 

pressure over a short time interval (0, tf) with tf << τ and heat is transferred by radiation only, 

equation 8 becomes 

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

⎥

⎦

⎤ ⎢

⎣

⎡

≈− ′′′ −−

a

f

af V

V

φ)(1Q lnP

ρc

1 TT (9) 

6
where Q ′ ′ ′ = tfQ ′′′ & (J/m3

) is the energy density at ignition. If the moles of reactants (fuel and air) 

and combustion products (CO2 and H2O, principally) are equal and behave as ideal gases, and Tf

is the (quasi) adiabatic flame temperature 

Q ′ ′ ′ = ρc(Tf − Ta ) + Pln Tf /Ta [ ]

1− φ (10) 

The lower flammability limit (LFL) is the minimum volume (or mole) fraction of fuel in a fuelair mixture that sustains ignition [11, 12, and 18]. The LFL has been measured for hundreds of 

gaseous and liquid hydrocarbon fuels, including fuels that contain oxygen, nitrogen, sulfur, 

boron, phosphorus, and halogen [11]. The average value of Q ′′′ for 236 combustible compounds 

is 

Q ′ ′ ′ = ρf hc

0

LFL =1864 ± 278 kJ

m

3 (11) 

where ρf and h are the vapor density and heat of complete combustion of the fuel, respectively. 

If burning occurs at the LFL of the fuel, then equations 10 and 11 are equal and 

c

0

ρc(Tf − Ta ) + Pln Tf /Ta [ ]

1− φ = 1.9 MJ

m3 (12) 

Equation 12 can be solved for the quasi-adiabatic flame temperature at standard temperature and 

pressure. For φ < 0.2, the calculated flame temperatures using equation 12 are in the range 

Tf = 1720 K - 1420 K, compared to experimental values Tf = 1600 ±100 K [11 and 12]. 

Equation 12 shows that the LFL corresponds to a temperature Tf ≈ 1600 K at which the rate of 

heat losses from the flame equal the rate of heat production in the flame due to the combustion 

reactions. 

2.2 THE MESOPHASE. 

The mesophase is the interface between the gas and condensed phases during burning. All the 

thermal degradation chemistry that results in volatile fuel generation occurs in the mesophase 

(also known as the pyrolysis zone). A qualitative diagram of the mesophase properties is shown 

in figure 4. The temperature distribution at the burning surface is primarily a consequence of the 

prevailing energy balance but the viscosity, density, and physical dimension of the mesophase 

shown qualitatively in figure 4 are determined by the temperature field and thermal degradation 

chemistry. For polymers that thermally degrade with the formation of a solid char, the viscosity 

of the mesophase is higher than the molten polymer and probably comparable to the solid 

polymer. The mesophase is comprised of thermal degradation products in a variety of phases, 

including gas, liquid, and solid, as indicated in figure 4 by the bubble density and in figure 5 by a 

generic product distribution. 

7
GAS MESOPHASE CONDENSED

Density, ρ

(log scale)

Temperature, T

Tp

ρg

Fuel-Air Mixture

Viscosity, γ

(log scale)

γg

Td

0 δ

Distance From Surface, x

Charring

Non-Charring

γc

FIGURE 4. MESOPHASE PROFILES OF TEMPERATURE, VISCOSITY, AND DENSITY 

DURING FLAMING COMBUSTION 

Polymer

+ O2

Combustible and 

non-combustible gases

Liquid products

Primary Char

 Thermal feedback from flame 

Fuel 

Gases

Secondary Char

CONDENSED 

PHASE

GAS PHASE

Flame

MESOPHASE

FIGURE 5. PHENOMENOLOGY OF POLYMER BURNING 

Figure 5 shows the phenomenology of polymer burning and illustrates the coupled nature of the 

flaming combustion of condensed phases. The sequence of events for self-sustained burning 

involves the application of heat sufficient to thermally degrade (pyrolyze) the solid polymer to a 

8
low molecular weight volatile fuel species and possibly a nonvolatile/solid char, depending on 

the polymer chemical structure. Mixing of the volatile thermal degradation products with 

atmospheric oxygen and ignition of this fuel and air mixture results in flaming combustion. 

Flaming combustion produces thermal energy in proportion to the heat of combustion of the 

volatile thermal degradation products and at a rate that is controlled by the fuel generation rate. 

The majority of the combustion energy from the flame is lost to the environment, but a fraction is 

returned to the polymer surface by convection and radiation (see figure 2). If the feedback of 

thermal energy from the flame at the polymer surface is sufficient to generate fuel vapors, 

flaming combustion will continue after the ignition source is removed and burning will be selfsustained. 

2.2.1 Kinetics. 

In figure 5, the first stage of thermal degradation produces primary volatiles (gas and liquid 

products/tar) and possibly a primary char residue (see section 4.5). If a primary char forms, 

further decomposition generates a secondary gas (principally hydrogen) and a thermally stable 

carbonaceous char. Figure 6 shows thermogravimetric analyzer (TGA) data at a heating rate of 

10 K/min for anaerobic pyrolysis of polybenzimidazole (2,2′-(m-phenylene)-5,5′-

bibenzimidazole). Polybenzimidazole is a heat-resistant, char-forming polymer that thermally 

degrades by primary and secondary decomposition events, as evidenced by the distinct mass loss 

rate peaks for these processes. Models have been proposed that account for some or all of the 

pyrolysis products (gas, tar, primary char, secondary char, and secondary gas) as various 

combinations of sequential or simultaneous thermal degradation reactions. However, a detailed 

mechanism for the thermal degradation of most polymers, especially char-forming polymers, is 

unlikely and unnecessary for a phenomenological treatment of fuel generation chemistry. 

0.0

0.05

0.10

0.15

0.20

0.25

500 550 600 650 700 750 800 850

Mass Loss Rate (mg/g-sec)

Temperature, °C

Primary 

Decomposition

Secondary 

Decomposition

FIGURE 6. FRACTIONAL MASS LOSS RATE VERSUS TEMPERATURE FOR 

POLYBENZIMIDAZOLE IN TGA (β = 10 K/min) 

Mechanistic reaction kinetics of polymer thermal degradation processes show that the overall 

mass loss (fuel generation) rate should be first order with respect to the instantaneous mass if the 

reactive intermediates (free radicals) maintain a steady-state concentration, regardless of whether 

9
thermal degradation occurs by random or end-chain scission. A first-order thermal degradation 

scheme that accounts for the main pyrolysis products is [4, 7, and 10]. 

Polymer (P) →

kd

Intermediate (I*) (13) 

I * →

kg

Gas (G) (14) 

Char(C) (15) 

k

*I c

→

Equations 13-15 are a subset of the reactions shown in figure 5, but they are sufficient to 

represent the mesophase fuel generation kinetics. In particular, polymer P thermally degrades to 

a reactive intermediate I* with rate constant kd. The intermediate produces gas G and/or char C, 

with rate constants kg and kc, respectively. Figure 7 shows data for a variety of pure, unfilled 

polymers plotted as the mass fraction of char measured immediately after flaming combustion 

has ceased in a fire calorimeter (see section 5.6) versus the char residue at 900 ±100°C for the 

same material after anaerobic pyrolysis in a TGA at a heating rate of about 10 K/min. It is seen 

that the char yield of a material in a fire is essentially equal to its residual mass fraction after 

anaerobic pyrolysis at temperatures representative of the char temperature in a fire. Although 

oxidative degradation products have been identified at the surface of olefinic polymers after 

flaming combustion, the data in figure 7 suggest that oxidation reactions in the solid during 

flaming combustion are not important to the overall fuel fraction. If the reactive intermediate I* 

in equations 13-15 is a stationary state, then dI*/dt = 0, and if thermal decomposition is an 

anaerobic process, the fuel generation rate is 

− dm'

dt = kpm' = Ae− Ea / RTm' (16) 

where m′ is the mass of volatile fuel, kp is the mass loss rate constant in terms of a global 

frequency factor A (1/s) and activation energy Ea (J/mole). Equation 16 is easily solved for the 

fuel generation rate at constant temperature (isothermal conditions). However, the polymer 

temperature changes rapidly from ambient to the pyrolysis temperature near the burning surface; 

thus, a nonisothermal solution of equation 16 is required to capture the dynamics of the fuel 

generation process as it occurs in the mesophase. For an arbitrary temperature history T(t) in the 

mesophase, the mass of fuel generated at any time t is 

∫ ⎥

⎦

⎤ ⎢

⎣

⎡

−−=⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ t

0

a dt'

)RT(t'

E Aexp (0)m'

m'(ττ ln (17) 

10
0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1.0

Fire Char Yield (g/g)

TGA Pyrolysis Residue (g/g)

FIGURE 7. CHAR MASS FRACTION IN FIRE VERSUS ANAEROBIC PYROLYSIS 

Equation 17 can be solved numerically for any specified temperature history. However, the 

mesophase temperature history is a function of both time and position (see figure 4); therefore, 

transient temperature distribution T(x,t) must be specified to obtain an analytic solution for 

equation 17. If the temperature distribution is static during steady burning of a thick sample as 

the surface x = 0 recedes at constant velocity v = (dx/dt)T and the mesophase is a thin surface 

layer, then the rate of temperature rise of the mesophase is constant, (dT/dt)x=0 = -v (dT/dx)t = β. 

The assumption of a constant heating rate for the mesophase transforms the independent variable 

in equation 17 from time to temperature and allows for a solution in terms of the mass fraction of 

polymer remaining at temperature, T. 

m(T)

m0

= μ(T) +[ ] 1− μ(T) e

−y

 (18) 

where y = kp RT2

β(Ea + 2RT)

The equilibrium char fraction is 

μ(T) = kc

kc + kg

= 1 +

Ag

Ac

exp −

Eg − Ec

RT

⎛ 

⎝ ⎜ ⎞ 

⎠ ⎟ 

⎡

⎣ 

⎢ ⎢ 

⎤

⎦ 

⎥ ⎥ 

−1

 (19) 

in terms of the frequency factors, Ag and Ac and the activation energies Eg and Ec, for gas and 

char formation, respectively. A temperature-dependent equilibrium char fraction that is the ratio 

of rate constants for gas and char formation is consistent with the use of group contributions for 

the char-forming tendency of polymers [22] (see section 4.5). The fractional mass loss rate at 

temperature T is obtained by differentiating equation 18 with respect to time. For μ(T) = μ = 

constant, the result is 

− 1

m0

dm

dt = ( ) 1− μ kp e

− y

 (20) 

11
Setting the time derivative of equation 20 equal to zero shows that the maximum fuel generation 

rate occurs when 

2

p

a

p

a

pp RT

E

RT

E expA)T(k β =

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡

−= (21) 

Substituting kp from equation 21 into equation 20 for Ea >> RTp gives the maximum fuel 

generation rate 

− 1

m0

dm

dt max

= ( ) 1 − μ βEa

eRTp

2 (22) 

The temperature Tp in equations 21 and 22 is the temperature at the maximum fuel generation 

rate during the course of the linear temperature history. Defining a characteristic heating rate, 

β* = A ΔTp where ΔTp = RTp

2

/Ea is the half-width of the pyrolysis temperature interval, equation 

22 takes the form of a (statistical) thermodynamic phase transition temperature. 

 Tp = Ea

R ln[β* /β]

 (23) 

TGA is a common laboratory method for studying the thermal degradation kinetics of polymers 

at a constant heating rate [6-10]. The maximum fuel generation rate and Tp are readily obtained 

from these experiments as shown in figure 8 for polymethylmethacrylate (PMMA) and 

polyamideimide (PAI). Figure 8 shows the onset thermal degradation temperature Td, the 

temperature at peak mass loss rate Tp, and the char fraction μ for PAI. The range of 

temperatures over which pyrolysis takes place is of the order eRTp /(1-μ)E 2

a, which is very 

different for these two polymers of widely differing thermal stability and charring tendency. 

Table A-1 in appendix A contains Td, Tp, and ignition temperatures for a number of polymers. 

2.2.2 Thermochemistry. 

The basic thermal degradation mechanism leading to volatile fuel generation in polymers 

involves primary and secondary decomposition events, as illustrated in figure 5. The primary 

decomposition step can be main-, end-, or side-chain scission of the polymer. Subsequent 

thermal degradation reactions depend largely on the chemical structure of the polymer but 

typically proceed by hydrogen transfer to α- or β-carbons, nitrogen or oxygen, intramolecular 

exchange (cyclization), side-chain reactions, small-molecule (SO2, CO2, and S2) elimination, 

molecular rearrangement, or unzipping to monomer [15]. Unzipping or depolymerization of 

vinyl polymers is characterized by a kinetic chain length or zip length that is the average number 

of monomer units produced by a decomposing radical before the radical is deactivated by 

termination or transfer. Mathematically, the zip length is the ratio of the rate constants for 

initiation to termination. 

12
Residual Mass Fraction 

(g/g)

0

1

2

3

4

5

0 200 400 600 800 1000

Temperature (°C)

0

0.2

0.4

0.6

0.8

1.0

1.2

PAI

PMMA

Fractional Mass Loss Rate 

(mg/g-s)

Td (PAI)

Tp (PMMA)

PAI

PMMA

Char 

Yield 

Td (PMMA) 

Tp (PAI) 

A 

B 

FIGURE 8. THERMOGRAVIMETRIC ANALYSIS DATA FOR PMMA AND PAI 

(a) RESIDUAL MASS FRACTION VERSUS TEMPERATURE AND 

(b) MASS LOSS RATE VERSUS TEMPERATURE 

Aromatic backbone polymers such as polycarbonate, polyimides, polyaramides, polyarylsulfones, 

and polyphenyleneethers tend to decompose in varying degrees to a carbonaceous char residue 

through a complex set of intramolecular rearrangements and side-chain reactions involving 

cross-linking and bond scission. The char yield is the mass fraction of carbonaceous char that 

remains after flaming combustion of the polymer. Charring competes with termination reactions 

that generate volatile species, thus reducing the amount of available fuel in a fire. In addition, 

char acts as a heat and mass transfer barrier that lowers the flaming HRR. Figure 7 demonstrated 

that the char yield in a fire is roughly equal to the anaerobic pyrolysis residue at high (flame) 

temperatures. Polymers that contain heterocyclic or aromatic structures in the backbone tend to 

form char during thermal decomposition in rough proportion to the carbon/hydrogen (C/H) ratio 

of the polymer. Figure 9 shows the mass fraction of char plotted versus the mole fraction of 

hydrogen in the polymer molecule. High C/H ratios favor termination by crosslinking between 

carbon radicals and char is formed. Low C/H ratios favor termination of carbon radicals by 

hydrogen transfer, resulting in low molecular weight fuel species rather than char. The relative 

rates of intermolecular cross-linking and aromatization and intramolecular hydrogen transfer and 

cyclization reactions, i.e., the ratio kc/(kc+kg) in equation 19, will determine the char yield at any 

particular hydrogen mole fraction. 

13
0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1.0

Char Mass Fraction at 800 °C

Hydrogen Mole Fraction in Polymer

PTFE

diamond

Intramolecular 

Reactions

Intermolecular 

Reactions

FIGURE 9. CHAR MASS FRACTION VERSUS HYDROGEN MOLE 

FRACTION IN POLYMER 

2.2.3 Energetics. 

In principle, the heat (enthalpy) of gasification is the difference between the enthalpy of the solid 

in the initial state at ambient temperature and pressure, T0 and P0, and the enthalpy of the volatile 

thermal decomposition products at Tp and P0. If the stored heat is ∆hs, the enthalpy of fusion 

(melting) for semicrystalline polymers is ∆hf, the bond dissociation enthalpy is ∆hd, and the 

enthalpy of vaporization of the decomposition products is ∆hv, then the enthalpy of gasification 

per unit mass of fuel is [10] 

 Lg = ∆hs + ∆hf + ∆hd + ∆hv = + c(T)dT ∆h T0

Tp

∫ f + ∆hd + ∆hv (24) 

The symbol Lg derives from latent heat, i.e., the recoverable heat in a reversible process. 

Thermolytic cleavage of primary chemical bonds in the polymer backbone to produce volatile 

fuel and char is obviously not a reversible process, but the symbol Lg will be used throughout to 

conform with the literature in the fire sciences. Table 1 illustrates the magnitude of these 

enthalpic terms for amorphous poly(methylmethacrylate), polystyrene, and semicrystalline 

polyethylene. The stored heat, ∆hs, was obtained by numerical integration of heat capacity 

versus temperature from ambient to the dissociation temperature as per equation 24. The 

dissociation (bond breaking) enthalpy, ∆hd, is assumed to be equal to the heat of polymerization 

but opposite in sign for these polymers, which thermally degrade by random or end-chain 

scission. The degradation product for polyethylene (PE) is assumed to be a tetramer (i.e., octane 

with Mg = 112 g/mole) for the purpose of calculating the heats of dissociation and vaporization 

on a mass basis for this polymer, and the degree of polyethylene crystallinity of PE is taken to be 

90%. All other enthalpies in table 1 were obtained from handbooks using monomer molecular 

14
weights to convert the energies to a mass basis. The values for hg in the second to last row were 

obtained by summing the individual enthalpies, according to equation 24, for each polymer. 

TABLE 1. COMPONENTS OF THE ENTHALPY OF GASIFICATION FOR 

PMMA, PS, AND PE 

PMMA PS PE 

Monomer MW (g/mole) 100 104 28 

Fuel MW (g/mole) 100 104 112 

∆hs (J/g) 740 813 803 

∆hf (J/g) amorphous amorphous 243 

∆hd (J/g) 550 644 910 

∆hv (J/g) 375 387 345 

Lg = Σ ∆hi (J/g) 1665 1850 2301 

Lg (measured) J/g 1700 1800 2200 

In practice, the enthalpy of gasification is rarely calculated because detailed and reliable 

thermodynamic data for the polymer and its decomposition products are generally unavailable. 

Direct laboratory measurement of Lg using differential thermal analysis and differential scanning 

calorimetry have been reported, but Lg is usually measured in a constant heat flux gasification 

device or fire calorimeter (see section 3.2). In these experiments, a plot of mass loss rate per unit 

surface area (mass flux) versus external heat flux has slope 1/Lg where 

Lg = hg

1−μ

 (25) 

hg is the heat of gasification per unit mass of solid and μ is the nonfuel fraction (char or inert 

filler). The last row in table 1 lists the average of hg values for these noncharring polymers. 

Agreement is quite good between experimental values and thermochemical calculations of hg. 

Table A-2 in the appendix A contains Lg, μ, and hg for 53 polymers. Analysis of the data in 

table A-2 shows that Lg and μ vary widely with polymer chemical structure, but hg is relatively 

independent of composition with an average value, hg = 2.0 ±0.5 kJ/g. 

2.3 THE CONDENSED PHASE. 

The rate at which heat is transported and stored in the condensed phase is of fundamental 

importance because these processes determine the time to ignition and burning rate of polymers. 

Table A-3 in the appendix A lists generic thermophysical properties at ambient temperature 

(295 ±3 K) gathered from the literature for a number of common thermoplastics, thermoset 

resins, elastomers, and fiberglass-reinforced plastics [4]. Entries are individual values, averages 

of values from different sources, or averages of a range of values from a single source and, 

therefore, represent in most cases a generic property value with an uncertainty of about 10%-

20%. 

15
Neglecting changes in the slope or magnitude of thermal properties that occur at phase changes, 

such as the glass transition, melting, and decomposition temperatures of polymers, the 

temperature dependence of κ, ρ, and c for an amorphous polymer can be roughly approximated 

κ(T) = κ0

T

T0

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

 (26) 

ρ(T) = ρ0

T0

T

⎡ 

⎣ ⎢ ⎤ 

⎦ ⎥ 

1

2

 (27) 

⎥

⎦

⎤ ⎢

⎣

⎡ =

0

0 T

T cc(T) (28) 

These properties are plotted in reduced form in figure 10 as P(T)/P(T0) versus T/T0, where P(T) 

and P(T0) are the values of κ, ρ, or c at temperature T and standard temperature (298 K), 

respectively. 

0

1

2

3

4

0

Reduced Property Value, P/P0

Reduced Temperature (T/T0)

1.0 2.0 3.0

0 200 400 600 800 1000

Temperature, T(K)

Heat 

Capacity

Thermal 

Conductivity

Density

FIGURE 10. TEMPERATURE DEPENDENCE OF POLYMER HEAT CAPACITY, 

THERMAL CONDUCTIVITY, AND DENSITY 

The product κρc is a quantity called the thermal inertia that emerges from the transient heat 

transfer analysis of ignition time (see equation 40). The temperature dependence of κ, ρ, and c 

in equations 26-28 suggest that the product of these terms (i.e., the thermal inertia) should have 

the approximate temperature dependence: 

κ(Τ) ρ(Τ) c(T) ≈ κ0ρ0c0 T/T0 = (κρc)0 T/T0 (29)

where κ0, ρ0, and c0 are the room temperature (T0) values listed in appendix A table A-3. 

16
Another thermal parameter that emerges from unsteady heat transfer analyses is the thermal 

diffusivity α = κ/ρc, which, according to equations 26-28, should be relatively independent of 

temperature 

 α(T) = )T(c)T(

)T(

ρ

κ

= α0 (30) 

Room temperature values of polymer thermal diffusivity are listed in appendix A table A-3. 

Another thermal property that affects the response of a polymer to the exposure from an external 

heat source is the surface absorptivity. It is generally assumed that polymers behave as gray 

surfaces, i.e., the total hemispherical surface absorptivity is equal to the total hemispherical 

emissivity, ε. Hallman [23] measured ε for many polymers and different radiant heat sources. 

Some of Hallman’s measurements are given in table A-4. These values are applicable prior to 

ignition, and it is reasonable to assume that ε =1 for the flaming surface of a polymer. 

3. FIRE BEHAVIOR OF SOLID POLYMERS.

The continuum level treatment of the fire behavior of polymers disregards the discrete 

(molecular) structure of matter so that the temperature distribution, and more importantly its 

derivatives, are continuous throughout the material. In addition, the polymer is assumed to be 

thermally thick and have identical properties at all points (homogeneous) and in all directions 

(isotropic). In this way, analytic results for ignition and burning can be derived from unsteady 

and steady heat transfer analyses, respectively, using simplified mass and energy balances. The 

continuum level treatment provides scaling relationships between the properties of polymers and 

their fire response but ignores many important characteristics of burning behavior, such as the 

effect of char formation on heat and mass transfer, swelling (intumescence), and dripping, that 

can only be captured empirically or through detailed numerical modeling and analyses. 

3.1 IGNITION. 

Ignition is the initiation of combustion of a fuel-air mixture that is uniformly heated 

(autoignition) or comes in contact with a flame, spark, or glowing wire (piloted ignition). The 

ignition of volatile liquid and gaseous fuels is fairly well understood because only the global or 

local thermodynamic state of the system needs to be considered [11 and 17-19]. As shown in 

section 2.1, the reaction of gaseous fuels with air will be self-sustaining if the combustion energy 

density of the mixture is above a minimum (critical) value of about 2 MJ/m3

. The burning of 

condensed phases is more complicated because there is dynamic coupling of heat and mass 

transfer between the gas phase and condensed (meso, solid) phase [11 and 12]. Consequently, a 

variety of criteria have been proposed for piloted ignition of solids, which can be roughly divided 

into thermal (condensed phase) and chemical (gas phase) [11 and 24]. The primary example of a 

thermal criterion is an ignition temperature for the solid, while chemical criteria extend to a 

critical mass flux or a critical HRR. Any of these criteria can be expressed in terms of an 

external heat flux at which the temperature or the flux of mass and energy reaches some critical 

value. The criteria for piloted ignition of polymer solids are examined separately below. 

17
3.1.1 Chemical Criteria. 

Chemical criteria for ignition of condensed phases include a boundary layer reaction rate and a 

critical mass flux of fuel gases, both of which are equivalent to establishing a LFL at the ignition 

source for a fixed test geometry and ventilation rate. Table 2 lists the mass fluxes at incipient 

piloted ignition and incipient burning or extinction for over 20 polymers measured in a fire 

calorimeter (section 5.6) or similar device. Also listed is the effective heat of combustion (HOC) 

of the fuel gases and the product of the mass flux and HOC at ignition or extinction, i.e., the 

HRR. The mass flux at ignition in table 2 varies between polymers because of differences in the 

LFL of their pyrolysis products or fuel gases. If piloted ignition occurs when the concentration 

of pyrolysis gases in air reaches the LFL of the particular fuel species and mf & ′′ and ma & ′′ are the 

mass fluxes of fuel and air in a well-mixed volume at the igniter, then for LFL << 1, 

LFL

ρ

ρ

LFL1

LFL

ρ

ρ

m

m

m

m

a

f

a

f

a

f

a

f ⎟ ≈

⎠

⎞ ⎜

⎝

⎛

− == ′′

′′

&

& (31) 

The average convective heat transfer coefficient at the polymer surface at incipient ignition is 

mch aa = & ′′ (32) 

The mass flux at ignition from equations 11, 31, and 32 is 

0 0

aa caa c

f

f LFL h

*HRR

h

1

ρ c

Qh LFL

c

h

ρ

ρ m = ′′′ & ′′ = = (33) 

TABLE 2. MASS LOSS RATE, EFFECTIVE HOC, AND HRR AT IGNITION (FLASH 

POINT) AND INCIPIENT BURNING/EXTINCTION (FIRE POINT) 

Flash Point Fire Point 

Polymer 

HOC 

(kJ/g 

MLR 

(g/m2-s) 

HRR 

(kW/m2)

MLR 

(g/m2

-s) 

HRR 

(kW/m2)

POM 14.4 0.88 13 1.7-4.5 40 

PMMA 24.8 0.97-1.01 25 1.9-3.2 61 

PE 40.3 0.88 35 1.3-2.5 73 

PP 41.9 0.60 25 1.1-2.7 72 

PS 27.9 0.57 16 0.8-4.0 50 

PS FR 9.6 2.0 19 6-8 67 

PUR 23.7 0.83 20 2.0 47 

PA6 29.8 0.88 26 3.0 89 

PBT 21.7 0.77 17 3.4 74 

PC 21.2 0.78 17 3.4 72 

PPS 23.5 0.81 19 3.6 85 

PPZ 15.4 1.23 19 3.0 46 

18
TABLE 2. MASS LOSS RATE, EFFECTIVE HOC, AND HRR AT IGNITION (FLASH 

POINT) AND INCIPIENT BURNING/EXTINCTION (FIRE POINT) (Continued) 

Flash Point Fire Point 

Polymer 

HOC 

(kJ/g 

MLR 

(g/m2-s) 

HRR 

(kW/m2)

MLR 

(g/m2

-s) 

HRR 

(kW/m2) 

PEN 22.9 0.71 16 2.7 62 

PEEK 21.3 0.72 15 3.3 70 

PESU 22.4 0.9 20 3.7 83 

EP 21.3 1.0 21 3.4 72 

CE 22.8 1.3 30 4.4 100 

PBI 16.2 1.5 24 − −

PI 12.0 1.30 16 4.0 48 

PEI 16.7 0.82 14 − −

PAI 19.3 1.63 31 2.5 48 

Average: 1.0 21 3.2 66 

Standard Deviation: 0.4 6 1.2 17 

Equation 33 shows that there is a parameter with the units and significance of a virtual HRR, 

HRR* = h Q / ′ ′ ′ ρa ca , that is independent of the type of polymer but depends on the nature of the 

convective environment, i.e., the test conditions. Piloted ignition of a solid polymer will occur 

under a particular set of test conditions when 

LFL 0

c

ign h

*HRR ′′ =mm && ′′ ≥ (34) 

or when 

 * ignc HRRmh0 & ′′ ≥ (35) 

In fire calorimeters (section 5.6), HRR* is of the order 

HRR* = h Q ′ ′ ′ 

ρa

ca

= (10W / m2 − K)(1.9 MJ/ kg)

(1kg / m3

)(1kJ/ kg − K) ≈ 20 kW

m2

Equations 34 and 35 are physically based criteria for ignition of polymers in typical (section 5.6) 

convective environments where a spark is located 25 mm from the heated polymer surface. 

Equation 35 is a steady-state, two-dimensional analog of the combustion energy density criterion 

for gaseous ignition (equation 11) and, like that criterion, is independent of the chemical 

composition of the fuel gases. Using HRR* = 20 kW/m2

 and the indicated HOC in table 2, 

equation 34 predicts m& ign ′′ = 1.00 ±0.37 g/m2

-s at the flash point, which is indistinguishable from 

the average experimental result. Equation 35 predicts that piloted ignition is imminent when 

mh ignc = HRR ≥ HRR* = 20 kW/m 0 & ′′ 2, which is also indistinguishable from the experimental 

19
result HRR = 21 ±6 kW/m2

 at incipient ignition (the flash point). Table 2 also lists the mass flux 

and HRR for the majority of polymers at the fire point when the flame is first established. The 

mass flux and HRR increase by a factor of 2-3 between the flash point and the fire point as 

additional heat flux is imparted to the surface from the flame at incipient burning. 

3.1.2 Thermal Criterion. 

A chemical criterion (equation 34 or 35) is probably sufficient for ignition to occur, but a surface 

temperature in the vicinity of the thermal decomposition temperature is necessary to begin the 

fuel generation process. The thermal theory of ignition assumes that the surface temperature at 

ignition is a characteristic property of the polymer. If fuel gasification obeys a simple energy 

balance, such as equation 24 and the temperature dependence of the heat capacity is equation 28, 

i.e., c(T) = c0T/T0, then the enthalpy of gasification at ignition is 

c0

T0

T dT + Δhf + Δhd

T0

Tign

∫ + Δhv = Lg (36) 

The heat capacity-temperature integral in equation 36 can be solved explicitly with the result 

c0Tign

2

2T0

+ Δhf + Δhd + Δhv − c0T0

2

⎛

⎝ ⎜ ⎞

⎠

⎟ = Lg (37) 

The data in table 1 suggest that (Δhf + Δhd + Δhv − c0T0/2) ≈ Lg/2, which allows equation 37 to be 

solved for ignition temperature, Tign.

Tign ≈ T0 Lg

c0

⎡ 

⎣ ⎢ ⎢ 

⎤ 

⎦ ⎥ ⎥ 

1

2

 (38) 

Figure 11 is a plot of measured surface temperature at piloted ignition in a fire calorimeter 

(section 5.6) or similar device over a range of external heat fluxes for polyphenylenesulfide 

(PPS), polycarbonate (PC), polycaprolactam (PA6), polystyrene (PS), polybutylene-terephthalate 

(PBT), polypropylene (PP), unsaturated polyester thermoset (UPT), and PMMA. The ignition 

temperature of each polymer is relatively independent of heat flux, per equation 38, which also 

accounts for the large differences between polymers (see table A-1). Using typical properties for 

commodity and engineering polymers 

 

Tign = T0Lg

c0

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

= (298K)(2MJ /kg)

1.5kJ/kg − K

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2 = 630K = 357 o

C

which approximates the ignition temperature of these materials in the lower part of figure 11. 

For a constant ignition temperature, unsteady heat transfer [4, 11, and 12] gives the time to 

ignition, tign, for a thermally thick sample at a constant external heat flux, qext & ′′

20
TRP

qq

t

1 ext loss

ign

′′ − ′′ = && (39) 

where 

TRP = πκρc

2 (Tign − T0 ) (40) 

is a quantity known as the thermal response parameter (TRP). Equation 39 states that a plot of 

the reciprocal square root of the time to ignition versus the external heat flux has a slope equal to 

the average value of the thermal response parameter. The product κρc in equation 40 is an 

effective property called the thermal inertia that can be approximated using equation 29 and 

tabulated values for κ, ρ, and c, (see table A-3) or from the thermal response parameter if Tign is 

measured separately or calculated (see equation 38 and section 4.4). The intercept /TRP of 

equation 39 can also provide an estimate of T

qloss & ′′

ign if an additional expression is introduced to 

account for the surface heat losses at incipient ignition. 

εσ(T)T(Thq )T

4

o

4 &loss ′′ 0ign ign −+−= (41) 

250

300

350

400

450

500

550

IGNITION TEMPERATURE, °C

EXTERNAL HEAT FLUX, kW/m2

10 20 40 60 80 100

PS

PPS

PP

PC

PBT

UPT, PMMA 

PA6

PPS

PC

PBT

PA6

PS

PP

PMMA

UPT

FIGURE 11. IGNITION TEMPERATURE VERSUS EXTERNAL HEAT FLUX FOR PPS, 

PC, PA6, PBT, PS, PP, UPT, AND PMMA 

For a thermally thin sample of thickness b and at low external heat fluxes near the critical value, 

the ignition time and external heat flux are related. 

ρbc )T(T

qq

t

1

0ign

ext loss

ign −

′′ − ′′ = && (42) 

21
Equations 39 and 42 state that tign → ∞ as qext &′′ → qloss &′′ at the flash point. In other words, the 

minimum (critical) value of the external heat flux that can cause ignition is 

( ) 4

0

4 = qCHF &loss ′′ (ignition) 0ign )T(Th εσ ign −+−= TT (43) 

At the fire point, flaming combustion is first established. If a flame covers a polymer surface 

having ε ≈ 1 and heat losses are by reradiation only from a surface for which the burning and 

ignition temperatures are the same, then the first term on the right-hand side of equation 43 is 

zero, and the critical heat flux (CHF) for burning is 

 (44) 4

lossb rerad σTq ign = qCHF & ′′ (burning) ≈ & ′′ =

Equations 43 and 44 explain why thermally stable and heat-resistant polymers with high thermal 

decomposition, ignition, and burning temperatures require a higher heat flux to ignite and burn. 

Figure 12 shows a plot of the critical heat flux versus the ignition temperature of common 

polymers measured separately. The solid line is calculated from the abscissa using equation 43 

and the dotted line using equation 44. Critical Heat Flux for Ignition , kW/m2

0

10

20

30

40

50

60

0 100 200 300 400 500 600 700 800

Ignition Temperature, °C 

Halogen containing

CHF 

(calculated)

CHFb 

(calculated)

FIGURE 12. CRITICAL HEAT FLUX VERSUS IGNITION TEMPERATURE 

3.2 STEADY BURNING. 

Once ignition is sustained and the burning rate reaches a constant value, the HRR (W/m2

) of the 

polymer in steady-flaming combustion is [4, 11, 12, 20, and 21] 

net

g

c

c q L

h mhHRR

0

0

χ= ′′ χ= && ′′ (45) 

22
where χ is the combustion efficiency in the flame and 

net ext flame qqqq loss ′′ = ′′ + ′′ − &&&& ′′ (46) 

is the net heat flux for steady-flaming combustion with qflame &′′ the total convective and radiative 

heat flux from the flame to the polymer surface (see figure 2). The dimensionless ratio of the 

HOC to the heat of gasification in equation 45 is the heat release parameter (HRP). 

χ

hc

0

Lg

= χ( ) 1−μ

hc

0

hg

 = HRP (47) 

Fire calorimetry [4, 11, 20, and 25] (section 5.6) is used to obtain HRP as the slope of HRR 

versus external heat flux, or as the ratio χ hc /L0

g = HOC/Lg, from individual measurements. 

Table A-5 in appendix A contains HOC and χ (≡ HOC/h ) for common polymers while the 

HRPs are listed in table A-6. The HOC of the fuel gases, , was measured separately in a 

pyrolysis-combustion flow calorimeter [26] (section 5.5.2). 

c

0

hc

0

Figure 13 shows representative HRR histories for thermally thick and thin samples of polymers 

that gasify completely or form a char during burning. It is apparent that none of these HRR 

histories show a constant (steady-state) value of HRR over the burning interval as presumed in 

equation 45. Consequently, an average HRR for the entire test or over some time interval is 

typically used in place of a steady HRR. In fact, the interpretation of time varying HRR histories 

is a subject of active research in fire science. The curves on the left-hand side of figure 13 are 

characteristic of noncharring (μ = 0) plastics of different thickness. The heat release histories for 

the charring plastics on the right-hand side of figure 13 show the typical peak in HRR soon after 

ignition followed by a depression in the HRR as the char layer forms and increases in thickness. 

The growing char layer insulates the underlying plastic from the surface heat flux so that the net 

heat flux at the in-depth pyrolysis front decreases with time. Char can also act as a mass 

diffusion barrier to the volatile fuel. Charring polymers can be linear, branched, or cross-linked 

thermoplastics, elastomers, or thermosets having amorphous or semicrystalline morphologies. 

Time Time

Time

Thick Sample 

(Non Charring) Thick Sample 

(Charring)

Intermediate 

Thickness 

(Non Charring)

Time

Thin Sample 

(Charring/ 

Non Charring)

HRR (Arbitrary Units) HRR (Arbitrary Units)HRR (Arbitrary Units) HRR (Arbitrary Units)

FIGURE 13. REPRESENTATIVE HRR HISTORIES IN FLAMING COMBUSTION FOR 

THICK AND THIN SAMPLES OF CHARRING AND NONCHARRING POLYMERS 

23
In all cases in figure 13, the time integral (area under the curve) the HRR history per unit mass of 

polymer consumed by burning is the effective heat of flaming combustion HOC (J/kg). The 

effective HOC is determined primarily by the fuel chemistry, ventilation rate, and combustion 

efficiency in the flame. Combustion efficiency is low when halogens are present in the polymer 

molecule or added as flame-retardant chemicals, when soot or smoke is produced in large yield, 

or when there is insufficient oxygen for complete conversion of the organic fuel to carbon 

dioxide and water. Flaming combustion efficiency appears to be relatively independent of the 

charring tendency of a polymer (compare tables A-2 and A-4 in appendix A). 

Figure 14 shows fire calorimetry data for the average HRR of plastics versus their char yield 

after burning or pyrolysis. The nonlinear dependence of HRR on char yield in figure 14 

indicates that charring suppresses the HRR more than can be accounted for by the fuel fraction 

alone (e.g., equation 47). In fact, charring correlates with thermal stability (Lg) and acts as a 

barrier to the transfer of mass and heat during burning, as illustrated in figure 13, all of which 

tend to reduce HRR. 

0

100

200

300

400

500

600

700

0 0.2 0.4 0.6 0.8 1.0

Average Heat Release Rate, kW/m2

Char Yield, g/g

PMMA

PEEK

PVC

PS

PP

PBO

PE

CEN

PI

PPO

PBT

PET

PC

PSU

PX

PPSU PBI

PESU

PEN

PAI

ABS

PEI

EP

PET

PA VE

FIGURE 14. AVERAGE HRR IN FLAMING COMBUSTION VERSUS CHAR 

YIELD OF POLYMERS 

3.3 UNSTEADY BURNING. 

Unsteady burning or transient ignition is the fire behavior that is most relevant to flammability 

tests [5, 25, and 27]. In flammability tests of flame resistance, a thin strip of polymer is typically 

subjected to a Bunsen burner flame for several seconds to force ignition, after which the sample 

is removed from the flame and the duration, extent, and characteristics of burning are recorded. 

Polymers that continue to burn after removal from the ignition source are considered relatively 

flammable, while polymers that self-extinguish are relatively flame resistant. Flame resistance is 

related to fire behavior by combining equations 45-47 and separating the HRR into unforced 

(HRR0) and forced (HRP ) components qext & ′′

HRR HRR0 qHRP ext = + &′′ (48) 

24
where the HRR in unforced flaming combustion, i.e., in the absence of an external heat flux, is 

HRR qq(HRP ) 0 flame loss = ′′ − && ′′ (49) 

Equation 49 states that the surface flame must provide all the energy to sustain burning in 

unforced combustion. However, qflame &′′ contains convective and radiative components and will 

depend on the size and orientation of the sample with respect to its flaming surface, while qloss &′′

depends on sample thickness and heat transfer boundary conditions for unsteady burning. 

Consequently, HRR0 is generally apparatus- or test-specific. The fire parameters HRP and HRR0

for a fire calorimeter (section 5.6) can be determined from the slope and intercept, respectively, 

of a plot of HRR versus external heat flux in a fire calorimeter, as shown in figure 15 for PA6 

data from two different sources [4]. 

0

500

1000

1500

2000

0 20 40 60 80 100 120

PA6

Heat Release Rate, kW/m2

External Heat Flux, kW/m2

HRR0

(kW/m2) HRP

230

148

14

21

Slopes = HRP 

Intercepts = HRR0 

FIGURE 15. HEAT RELEASE RATE VERSUS EXTERNAL HEAT FLUX DATA 

FOR PA6 FROM DIFFERENT SOURCES 

If extinction occurs when the gas phase combustion energy density falls below a minimum 

(critical) value, analogous to the phenomenon that governs ignition, then equations 38 and 48 

provide a criterion for flame extinction in a flammability test. After the sample ignites and the 

flame is removed = 0, the sample will self-extinguish if qext & ′′

 HRR0 < HOC mb & ′′ = HRRb* (50) 

where m& b

′′ and HRRb* are the critical mass flux and HRR for sustained burning, respectively, in 

the flammability test (see equations 36-38). From equations 49 and 50, the flame heat flux at the 

fire point is 

loss

b

flame q HRP

*HRR & ′′ )extinction(q ≤ + & ′′ (51) 

25
Since HRRb* is test-dependent, the same value that governs horizontal burning and extinction in 

fire calorimeters (HRRb* ≈ 70 kW/m2

, see table 2) will not necessarily apply to extinction in an 

upward flame spread test of a thin strip of polymer. Table A-6 in appendix A lists HRR0 for 

common polymers along with their flammability rating in the Underwriters Laboratory vertical 

or horizontal (UL V, UL H) burning tests for flammability of plastic materials (a Bunsen burner 

ignition test). Table A-6 shows that when HRR0 < 50 kW/m2

, as measured in a fire calorimeter, 

self-extinguishing behavior is observed exclusively in the UL V burning test. Equation 49 shows 

that HRR0 decreases as the difference between the heat influx from the flame and the heat efflux 

by reradiation. Negative HRR0 values towards the bottom of table A-6 are observed for halogencontaining and flame-retarded plastics that may burn with a low flame heat flux. Negative HRR0

are also observed for heat-resistant and thermally stable polymers that have high losses and a 

thermally insulating char. In either case, qflame &′′ can be less than qloss &′′ and negative HRR0 are 

expected and observed. 

Another widely used flammability test is the limiting oxygen index (LOI) [25] test (section 5.5.1). 

The LOI is a downward-burning test of a thin (3- by 6- by 150-mm) polymer strip in a flowing 

gas stream whose oxygen concentration is adjusted until the sample flame is on the verge of 

extinguishing. The dependent variable in the LOI test is the flame heat flux, which increases in 

rough proportion to the oxygen concentration in the combustion atmosphere (independent 

variable). The concentration of oxygen in the combustion atmosphere at incipient burning and 

extinction is the LOI, and this corresponds to a flame heat flux in equation 51. 

loss

b

flame q HRP

*HRR

∝ & ′′ )extinction(qLOI = + & ′′ (52)

A value HRRb* ≈ 100 kW/m2

 has been observed for the LOI test. This value is somewhat higher 

than the critical HRR for incipient burning and extinction of horizontal slabs (HRRb* ≈ 70 

kW/m2

, see table 2) and upward burning of vertical strips (HRRb* ≈ 50 kW/m2) because heat 

transfer from the flame is less efficient in downward burning; thus, a higher HRR is necessary 

for sustained ignition in the LOI test. 

The equations for ignition, steady burning, and unsteady burning show that flammability tests 

measure the fire behavior of the polymer in unforced burning, whether as an after-flame time in a 

Bunsen burner test (section 5.4) or as an oxygen concentration at incipient extinction 

(section 5.5). Substituting equations 44 and 38 into equation 51 or 52 gives the efficiency of 

heat transfer from the flame to the polymer surface in terms of the fire parameter HRP. 

HRP

λ 1

HRP

HRR

q n)(extinctio

*

b

flame

+

= & ′′ (53) 

where λ= (σ/HRRb*)(χh Tc

0

0/c0)

2

 is a dimensionless quantity that is test-dependent by virtue of χ

and HRRb*. Appendix A table A-6 shows that self-extinguishing behavior in the UL 94 V test 

and an LOI above 30 is observed exclusively for HRP ≤ 5 in these tests where HRRb* = 75 ±25 

kW/m2

. Substituting HRP = 4.5 ±0.5 into equation 53 for typical λ = 20 ±5 (see tables A-2, A-3, 

26
and A-5) gives q&flame ′′ /HRRb* ≈ 0.8 at incipient extinction in tests of flame resistance. Thus, at 

incipient extinction and burning, when the combustion zone of the flame is in close proximity to 

the sample surface, a large fraction (≈ 80%) of the heat released by combustion is used to sustain 

the burning process. 

4. CHEMICAL STRUCTURE AND FIRE PROPERTIES. 

A powerful tool to study the effect of chemical structure on the properties of polymers is the 

additivity principle. The additivity principle, pioneered by Van Krevelen [22], assumes that 

polymer properties, when expressed per mole of substance, can be calculated by summation of 

atomic, chemical group, or bond contributions: 

P =ni Pi

j

∑

where P is a molar property, ni is the number of moles of component i in the polymer repeat unit 

contributing to the property, and Pi is the numerical value of the contribution. In the study of fire 

behavior, the use of specific (mass-based) properties, p, is more convenient and are related to the 

molar properties and molecular weight M of the repeat unit 

p = 

P

M =

ni

Pi

j

∑

niMi

j

∑

where Mi is the molar mass of component i. Additive molar contributions to polymer fire 

properties κ, ρ, c, hc,p , T 0

p, and μ are well documented, and their calculation from molar group 

contributions is straightforward. However, it is often the case that the molar group contributions 

are not available in the literature for new polymers with novel backbone and pendant structures. 

Recognizing this limitation of Van Krevelen’s group contribution method, Bicerano [28] 

generalized the additive scheme using graph theory to develop atomic connectivity indices, 

which replaced the larger chemical groups in the traditional additive approach as the principle 

descriptors of the topology of the polymer repeat unit. Bicerano’s approach is still empirical in 

that the connectivity indices must be determined from experimental data or by correlation with 

known group contributions. However, once the connectivity indices are determined for a 

particular property, that property may be predicted for any chemical structure for which the 

atomic (as opposed to group) composition is known. The connectivity index method of 

predicting polymer properties from atomic composition can be accomplished with a hand 

calculator but is more typically implemented using a stand-alone computer code or accessed as a 

module in molecular modeling software. Reactive molecular dynamics (RMD) simulations of 

thermal degradation is a semiempirical method that has recently been applied to the calculation 

of fuel species and fuel generation rates of polymers [10]. RMD simulations are the most 

fundamental and powerful approach to understanding and predicting polymer flammability 

because, unlike the additive approaches, RMD has the potential to predict the products and rates 

of thermal decomposition, i.e., the fuel generation chemistry. 

27
4.1 HEAT TRANSPORT. 

There are no good fundamental theories to predict the thermal conductivity κ (W/m-K), heat 

capacity c (kJ/kg-K), or density ρ (kg/m3

) of condensed phases (e.g., solid or molten polymers) 

from chemical structure, but an empirical structure-property correlation allows calculation of 

these properties from additive atomic or chemical group contributions if the chemical structure 

of the polymer is known. Table A-3 in appendix A lists the thermal properties of polymers, 

some of which were calculated from the chemical structure using additive contributions [22 and 

28] when experimental values were not available. 

4.2 HEAT OF COMBUSTION. 

Thermodynamics allow calculation of the heat of combustion, h , as the difference between the 

free energy of the products and reactants in equation 4. Additive molar contributions to the free 

energy of gaseous, liquid, and solid fuels have been tabulated and used successfully to estimate 

HOC. A simpler method for calculating or measuring combustion heat is based on the 

observation that the net heat of complete combustion of organic fuels per mole of oxygen 

consumed is independent of the chemical composition of the fuel [20] 

c

0

2

0

c

OO

c Og/kJ7.01.13

r

h

Mn

nM hC

0

22

0

−±==

⎥

⎥

⎦

⎤

⎢

⎢

⎣

⎡ = (54) 

where h is the net heat of complete combustion of the fuel with all products in their gaseous 

state, n and M are the number of moles and molecular weight of the molecule or polymer repeat 

unit, respectively, nO2

 is the number of moles of O2 consumed in the balanced thermochemical 

equation, and r

c

0

0 is the stoichiometric oxygen-to-fuel mass ratio. To illustrate the thermochemical 

calculation of the net heat of combustion, consider PMMA, which thermally degrades by endchain scission, unzipping, or depolymerization to monomer in quantitative yield. PMMA has the 

chemical structure 

CH3

CH2

O

C O

CH3

[ ]n C

Poly(methylmethacrylate)

The methylmethacrylate (MMA) repeat unit in brackets is the volatile fuel species when PMMA 

burns and has the atomic composition C5H8O2; therefore, the balanced chemical equation for 

complete combustion of PMMA is 

C5H8O2 + 6 O2 → 5 CO2 + 4 H2O 

28
Thus, six moles of O2 are required to completely convert one mole of PMMA repeat unit to 

carbon dioxide and water. Inverting equation 54, the HOC of the MMA fuel is 

kJ/g25.15 mole(1 MMA)(100 gMMA/mole)

/mole)Og)(32Omole)(6OkJ/g(13.1

nM

Mn

Ch OO 2 2 2 c

0 22 = − ⎥ =

⎦

⎤ ⎢

⎣

⎡ = (55) 

Net heats of complete combustion of polymers are available in the literature. If the mass fraction 

of char that remains after burning is μ, the fuel fraction is (1-μ), and the heat of complete 

combustion of the fuel gases, h , is related to the HOC of the char, h , and polymer, h , c

0

c ,μ

0

c,p

0

 hc

0

= hc,p

0

−μhc,μ

0

1−μ

 (56) 

Experimental values for h determined by pyrolysis-combustion flow calorimetry (section 5.5.2) 

are listed in appendix A table A-5. The elemental analysis of chars gives the typical chemical 

formula C

c

0

5H2 from which the HOC of the char calculated from oxygen consumption is 

≈ 37 kJ/g, which can be used to estimate the HOC of the fuel gases of charring polymers 

using equation 56 if μ is known. 

hc ,μ

0

4.3 ENTHALPY OF GASIFICATION. 

In principle, the enthalpy of gasification, Lg, could be estimated from chemical structure using 

additive molar contributions or estimated from equation 25 if μ is known and hg is taken to be 

2 MJ/kg. Also relevant to the energetics of fuel generation is the observation that the activation 

energy for pyrolysis Ea (J/mole) -measured laboratory TGAs approximates the molar enthalpy of 

gasification, if Mg is the molecular weight of the fuel gases [10] 

Lg = Ea

Mg

 (57) 

If M is the molar mass of the polymer repeat unit, it follows from equation 57 that the ratio 

Mg

M = EaMLg

 (58) 

should be characteristic of the mode of thermal degradation. For example, polymers, such as 

PMMA, polyoxymethylene (POM), and to a first approximation, PS, that thermally degrade by 

end-chain scission (depolymerize or unzip) produce monomer at near-quantitative yield. 

Consequently, these polymers should have Mg ≈ M or Mg/M ≈ 1. Polymers such as PE and PP 

that decompose by main-chain scission (cracking) to multimonomer fragments will have 

Mg/M > 1. Conversely, polymers with complex molecular structures and high molar mass repeat 

units (M ≥ 200 g/mole), such as polyamides (PA), cellulose, polyethyleneterephthalate (PET), or 

PC, that degrade by random scission, cyclization, small molecule splitting, or by chain-stripping 

29
of pendant groups such as polyvinylchloride (PVC) yield primarily low molar mass species 

(water, carbon dioxide, alkanes, and mineral acids) relative to the repeat unit so that for these 

materials Mg/M < 1. Table 3 shows fuel and monomer molar mass ratios, Mg/M, calculated as 

Ea/MLg, according to equation 58, for some of the polymers in table A-2. Global pyrolysis 

activation energies for the thermally stable engineering plastics listed in the last four rows of 

table 3 are estimated to be in the range Ea = 275 ±25 kJ/mole. Qualitative agreement is observed 

between the modes of pyrolysis (end-chain scission, random scission, and chain-stripping) and 

the calculated fragment molecular weight using equation 58, suggesting that the global pyrolysis 

activation energy determined from thermogravimetry experiments approximates the molar 

enthalpy of pyrolysis of the degradation products. 

TABLE 3. HEATS OF GASIFICATION, PYROLYSIS ACTIVATION ENERGY, CHAR 

YIELD, AS WELL AS CALCULATED AND MEASURED MOLECULAR WEIGHTS OF 

DECOMPOSITION PRODUCTS FOR SOME POLYMERS 

Polymer 

M 

(g/mol) 

Lg

(kJ/g) 

μ 

(g/g) 

hg

(kJ/g) 

Ea

(kJ/mol) Mg/M 

Pyrolysis 

Products 

Chain Cracking 

PP 42 1.9 0 1.9 243 3.0 C2-C90 saturated and 

unsaturated 

PE 28 2.2 0 2.2 264 4.3 hydrocarbons 

Unzipping 

PS 104 1.8 0 1.8 230 1.2 40%-60% monomer 

PMMA 100 1.7 0 1.7 160 0.94 100% monomer 

POM 30 2.4 0 2.4 84 1.2 100% monomer 

Intramolecular Scission 

PA 66 226 2.1 0 2.1 160 0.3 H2O , CO2 , C5 HC’s 

PVC 62 2.7 0.1 2.4 110 0.7 HCl, benzene, toluene 

Cellulose 162 3.2 0.2 2.6 200 0.5 H2O , CO2 , CO 

PT 131 5.0 0.6 2.0 178 0.3 

PC 254 2.4 0.3 1.7 200 < 1 

PEI 592 3.5 0.5 1.8 ≈ 275 < 1 

PPS 108 3.8 0.5 1.9 ≈ 275 < 1 

PEEK 288 3.4 0.5 1.7 ≈ 275 < 1 

PAI 356 4.8 0.6 1.9 ≈ 275 < 1 

PX 180 6.4 0.7 1.9 ≈ 275 < 1 

Complex mixture of 

low molecular weight 

products 

4.4 IGNITION TEMPERATURE.

Common sense and much experimental data suggest that the ignition temperature and thermal 

decomposition temperature of polymers should be related since mass loss and fuel generation 

begins in earnest at these temperatures. However, the heating rate in a fire is on the order of 10-

20 times higher than the heating rates normally used to measure thermal decomposition 

temperatures in laboratory thermogravimetry experiments. Figure 11 and equation 38 show that 

30
the ignition temperature of polymers is not particularly sensitive to heat flux (heating rate), while 

equation 23 states that the thermal decomposition temperature of polymers in TGA experiments 

increases by about 45°C for each 10 fold increase in heating rate. Consequently, there should be 

a heating rate βign in a TGA experiment for which the ignition and decomposition temperatures 

of polymers are equal, i.e., Tign = Tp(βign). Substituting equation 57 into equation 38 

 Tign = T0 Lg

c0

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

= T0 Ea

Mg c0

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

 (59) 

Setting this result equal to Tp in equation 23 

T0Ea

c0 Mg

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

= Ea

R ln(β*/βign )

 (60) 

Equation 60 can be evaluated at T0 = 293 K using the properties in table 4, with the result that 

the heating rate for which Tign = Tp(βign) is of the order 

βign = β * exp − Ea c0 Mg

R2 T0

⎡ 

⎣ 

⎢ ⎢ 

⎤ 

⎦ 

⎥ ⎥ 

1

2

 ≈ 1-3 K/min (61) 

which is at the lower range of heating rates typically used in nonisothermal TGA experiments, 

β = 10-20 K/min. From equations 59-61, the ignition and decomposition temperatures are 

related. 

1

Tign

= 1

Tp

+

R ln(β/βign )

Ea

TABLE 4. THERMOKINETIC PROPERTIES OF PMMA, PE, AND PHENOLIC TRIAZINE 

Polymer ln[β*,K/s] 

c0

(kJ/kg-K) 

Ea

(kJ/mole) 

Mg

(kg/mole) 

PMMA 30 1.4 160 0.10 

PE 43 1.5 264 0.11 

Phenolic Triazine 36 1.5 178 0.12 

Consequently, Tp measured in a TGA in an inert environment at heating rates β/βign ≈ 10 can be 

25-50 K higher than the ignition temperature (see table A-1) for typical Ea ≈ 200 kJ/mole. 

Figure 16 shows a plot of the data in table A-1 for the measured ignition temperature of 

polymers versus their mean thermal decomposition temperature (Td + Tp)/2. The use of a mean 

thermal decomposition temperature rather than Tp as an estimate of Tign compensates for most of 

the heating rate effects described by equations 59-61. Also contained in figure 16 are data for 

31
the incipient burning (fire point) and incipient ignition (flash point) temperatures of hydrocarbon 

oils plotted on the ordinate and abscissa, respectively. 

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800

IGNITION/FIRE POINT TEMPERATURE, °C

Oils

slope = 1.0 

r2 = 0.92

Solid 

Plastics

Halogen containing

DECOMPOSITION/FLASH POINT TEMPERATURE, °C

FIGURE 16. IGNITION/FIRE POINT TEMPERATURE VERSUS DECOMPOSITION/ 

FLASH POINT TEMPERATURE FOR SOLID AND LIQUID FUELS 

Because of its importance to flammability, Van Krevelen identified a number of experimental 

indices that can be used to characterize the short-term thermal stability of a polymer [22]. The 

indices, which are determined from temperature scanning thermogravimetry experiments at 

constant heating rates of 3-10 K/min are Td, the temperature in Kelvin at which the polymer 

weight loss is just measurable; Td,1/2, the temperature at which the weight loss reaches 50% of its 

final value; Td,max, the temperature at the maximum rate of weight loss; and Ea, the activation 

energy for pyrolysis. Noting that all of these temperatures depend on heating rate and that Td,max

is identical to Tp in the present work, Van Krevelen proposed the following interrelationships 

based on tabulated data for 37 polymers (all temperatures are Kelvin): 

 Td = 0.9 Td,1/2 (62) 

 Td, max = Tp

≈ Td,1/2 (63) 

 Tp ≈ 423 + Ea (kJ/mole) (64) 

Equation 64 can be cast in the form of equation 23 by defining a reference temperature T0 = Ea/R 

ln(β*/β0) = 423 K. Equations 62-64 imply that Tp or Td,1/2 can be used as the primary indicator 

of thermal stability with the other indices being roughly estimated from it. A plot of Tp versus Ea 

from thermogravimetric analyses of various polymers at heating rates on the order of 10 K/min is 

shown in figure 17. The trend is in qualitative agreement with equation 64 but the correlation 

coefficient is too low (< 0.5) for predictive purposes. For this reason, Van Krevelen extended 

the use of additive molar group contributions to the calculation of the thermal decomposition 

temperature. In Van Krevelen’s method of calculating the thermal decomposition temperature, 

32
the molar thermal decomposition function Yd,1/2 is related to the product of the polymer repeat 

unit molecular weight M and the decomposition temperature viz. 

M⋅Td, 1/2 = Yd, 1/2 (65) 

400

600

800

1000

1200

100 150 200 250 300 350 400

Decomposition Temperature, Tp (K)

Activation Energy for Pyrolysis, Ea (kJ/mol)

FIGURE 17. PYROLYSIS TEMPERATURE VERSUS ACTIVATION 

ENERGY OF POLYMERS 

The decomposition temperature is calculated by summing the individual molar decomposition 

functions Yd, 1/2

i for each chemical group of molar mass Mi comprising the repeat unit 

Td,1/ 2 = Yd,1/ 2

M =

niYd,1/ 2

i

j

∑

niMi

j

∑ (66) 

The molar group contribution Yd, 1/2

i for each of the chemical groups comprising the polymer 

were determined for decomposition temperatures measured at a linear heating rate ≈ 3 K/min. 

For example, the decomposition temperature of 2,2'-m-phenylene-5,5'-bibenzimidazole (PBI), 

having the chemical repeat unit structure 

N

N N

N

H

H

n

is calculated from the Yd, 1/2

i in table 5 and equation 66 as 

Tp = (2)(105) + (1)(65)

(2)(116.12) + (1)(76.09)

 x 1000 = 892 K = 619°C

which is in general agreement with the literature value Tp ≈ 903 K and the data in table A-1 and 

figure 6. 

33
TABLE 5. GROUP CONTRIBUTIONS TO THE DECOMPOSITION TEMPERATURE OF 

POLYBENZIMIDAZOLE 

Structural Group, i ni

Mi

(g/mole)

Yi

d,1/2 

(g-K/mole)

2 116.12 105 

1 76.09 65 

4.5 CHAR YIELD. 

Pyrolysis/char residue has the character of a thermodynamic quantity since it depends only on 

temperature and the composition of the material through the enthalpy barriers to gas and char 

formation, Eg, and Ec, in equation 19. The char-forming tendency of different groups is additive 

and roughly proportional to the aromatic (i.e., nonhydrogen) character of the group (see figure 9). 

The char yield is calculated by summing the char-forming tendency per mole of carbon of the 

chemical groups CFT,i and dividing by the molecular weight of the repeat unit [22]. 

Yc = CFT

M

x Mcarbon =

niCFT ,i

j

∑

niMi

j

∑ x12 (67) 

The CFT,i are the moles carbon remaining as char per mole of chemical group i in the polymer 

measured at 850°C. Negative corrections are made for aliphatic groups containing hydrogen 

atoms in proximity to char-forming groups because of the possibility for disproportionation and 

subsequent volatilization of hydrogen-terminated chain fragments that are no longer capable of 

recombining and cross-linking to make char. Table 6 lists the char-forming tendency of the 

structural units comprising bisphenol-A polycarbonate whose chemical structure is 

From the data in table 6 and equation 67, the char yield of polycarbonate is calculated to be 

Yc = (2)(4) + (1)(−3) + (1)(0) + (1)(0)

(2)(76) + (1)(42) + (1)(16) + (1)(44)

x 12 = 0.24 = 24% 

which compares with the measured value Yc = 0.25 in appendix A, table A-2. The method is 

empirical and relatively simple to use, and good agreement is obtained with other measured 

pyrolysis residues in table A-2. The char yield of polymers under anaerobic conditions is well 

described using the additive molar contributions of the individual structural groups comprising 

the polymer. 

34
TABLE 6. GROUP CONTRIBUTIONS TO THE CHAR YIELD OF BISPHENOL-A 

POLYCARBONATE 

Structural 

Group, i ni

Mi

(g/mole) 

CFT,i

(mole-C/mole) 

2 76.10 4 

C

CH3

CH3

1 42.08 -3 

C

O

O 1 44.01 0 

O 1 16.00 0 

4.6 HEAT RELEASE RATE. 

Individually, the material and combustion properties κ, ρ, c, hc,p , T 0

p, and μ have found limited 

success as descriptors of fire behavior because the coupling of gas and condensed phase burning 

processes are complex (e.g., figure 2). Direct measurement of fire behavior or flammability 

requires about one kilogram of material from which to prepare samples and is, therefore, 

prohibitively expensive for research where only gram quantities are typically available. Separate 

determination of thermochemical and combustion properties using laboratory thermal analyses 

and combustion calorimetry requires only gram quantities of material, but the process is time 

consuming. Consequently, recent work has focused on identifying a flammability parameter that 

captures the chemical dynamics of flaming combustion in a single laboratory test using research 

(gram) quantities of material [10, 26, and 29]. 

The HRR in flaming combustion HRR is the amount of heat, Q, released by gas phase 

combustion of unit mass of fuel, m, released by pyrolysis per unit time, t, and per unit area of 

burning surface, S. A simple dimensional analysis gives 

Qc ρδ dt

dQ

m

1 ρδ dtdQ

S

1 HRR & ⎟ =

⎠

⎞ ⎜

⎝

⎛ == (68) 

where ρ and δ are the average density and thickness of the mesophase, respectively. If a specific 

HRR is defined, that is, equation 22 multiplied by the HOC of the pyrolysis and fuel gases, 0

h c

2 c

p

c a c βη eRT

μ)E(1h Q β

0

=⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ − = & (69) 

where 

ηc = hc

0

(1 − μ)Ea

eRTp

2 ≈ hc, p

0

ΔTp

 (70) 

35
is a collection of thermal and combustion properties with the units (J/kg-K) and significance of a 

heat release capacity. The heat release capacity is the maximum amount of heat released by 

combustion per degree of temperature rise per unit mass of polymer in the mesophase. If the 

heating rate in the mesophase is β, then ηc is related to HRR. 

 HRR = ηc (χρδβ) = ηc f( qnet &′′ ) (71) 

where f( q& net ′′ ) = χρδβ is an increasing function of the external heat flux with units of kg-K/m2

-s. 

Figure 18 is a plot of the average HRR at an external heat flux of about 50 ±10 kW/m2

 versus ηc

for the same or similar polymers. The proportionality between HRR and ηc in figure 18 is 

reasonably good considering that the coefficient of proportionality f( qnet &′′ ) = f( ext flame qqq loss ′′ + ′′ − &&& ′′ ) 

varies with thermal stability, char-forming tendency, mesophase density, and flaming 

combustion efficiency in a complex way. 

10

100

1,000

10,000

10 100 1,000 10,000

Heat Release Capacity, J/g-K

Heat Release Rate, kW/m2

FIGURE 18. AVERAGE HRR VERSUS HEAT RELEASE CAPACITY OF POLYMERS 

Equation 70 is an explicit result for a parameter, ηc, that contains most of the properties known 

to correlate with flammability. In particular, ηc is proportional to the fuel fraction and HOC of 

the fuel and inversely proportional to thermal stability (heat resistance). Because ηc is a 

combination of material properties, each of which is calculable from additive molar group 

contributions, ηc itself should be calculable from the same or similar molar groups if it is a 

material property. 

From the additivity principle for polymer properties, a molar heat release capacity, Ψ, is defined 

[29] with units of J/mole-K whose functional form is equation 70 but with the thermal stability 

and combustion properties written as additive molar quantities, H, V, E, and Y/M in place of h , 

(1-μ), E

c

0

a, and Tp, respectively. If each chemical group i in the polymer adds to the component 

36
molar properties according to its mole fraction ni in the repeat unit, then in terms of molar 

quantities, equation 70 becomes 

 

Ψ = HVE

eR(Y/M)

2 =

ni

Hi

i

∑

⎛

⎝ ⎜ ⎜ 

⎞

⎠ ⎟ ⎟ ni

Vi

i

∑

⎛

⎝ ⎜ ⎜ 

⎞

⎠ ⎟ ⎟ ni

Ei

i

∑

⎛

⎝ ⎜ ⎜ 

⎞

⎠ ⎟ ⎟ 

eR ni

Yi / Mi

i

∑

⎛ 

⎝ ⎜ ⎜ 

⎞ 

⎠ ⎟ ⎟ 

2 (72) 

with Hi, Vi, Ei, Yi, and Mi the molar heat of combustion, mole fraction of fuel, molar activation 

energy, molar thermal decomposition function, and molar mass of component i, respectively. 

Expanding the summations in equation 72 and retaining only the noninteracting terms for which 

i = j = k... (i.e., neglecting terms containing products and quotients with mixed indices), the heat 

release capacity on a mass basis is 

 

ηc = Ψ

M =

ni

Ψi

j

∑

niMi

j

∑ =

Ni

Ψi

j

∑

NiMi

j

∑ (73) 

Experimental heat release capacities, ηc, have been measured for over 200 polymers, and the 

results were used to generate over 30 additive molar group contributions by treating the Ψi as 

adjustable parameters in equation 73 for polymers with known chemical structures [29]. 

Table A-6 in appendix A contains ηc for a few dozen polymers. Figure 19 compares calculated 

and measured heat release capacities for 50 polymers using the 30 empirical Ψi, determined by 

Walters and Lyon (2003). Overall agreement between measured and calculated values is about 

15%, which is encouraging at this early stage of research. Additive contributions to the heat 

release capacity are being updated as more polymers are tested and the measurement technique 

improves. As an example of the additive procedure for calculating the heat release capacity, the 

chemical repeat unit for PET is 

O C

O

C

O

O CH2CH2

for which the most recent chemical group contributions are listed in table 7. Combining the Ni, 

Mi, and Ψi for PET, per equation 73 

ηc = ∑Ni

Ψi

∑NiMi

= (1)(28.8) + (2)(0) + (2)(16.7)

(1)(76.10) + (2)(44.01) + (2)(14.03) = 62.2 kJ / mole − K192.18g / mole = 324 kJkg − K

The predicted heat release capacity for PET compares favorably with typical experimental values 

for this polymer ηc = 326 ±52 kJ/kg-K (see table A-6), considering that the group contributions 

are average values derived from several different polymers. 

37
0

300

600

900

1200

1500

1800

0 300 600 900 1200 1500 1800

Heat Release Capacity (Measured)

Heat Release Capacity (Calculated)

All Values J/g-K

FIGURE 19. POLYMER HEAT RELEASE CAPACITIES: CALCULATED VERSUS 

MEASURED VALUES 

TABLE 7. GROUP CONTRIBUTIONS TO THE HEAT RELEASE CAPACITY OF PET 

Structural 

Group, i ni

Mi

(g/mole) 

Ψi

(kJ/mole-K) 

1 76.10 28.8 

C

O

O 2 44.01 0.0 

CH2 2 14.03 16.7 

4.7 FLAME RESISTANCE. 

Flame resistance is the ability to withstand flame impingement or give protection from it. 

Equation 53 shows that a critical HRR criterion for incipient burning and extinction gives a 

simple scaling relationship between flame resistance and fire behavior in terms of the HRP. At 

the molecular level, HRR is governed by the heat release capacity (section 4.6), which is 

proportional to HRR in steady burning (equation 71) for a particular set of test conditions and 

material properties. Heat release capacity can be related to flame resistance in the same way that 

HRR was related to flame resistance (section 3.3). If the HRR is equation 71 and the criterion 

for flame extinction in flammability tests is equation 50, then flame extinction is related to heat 

release capacity. 

HRR = η ′

flamec

′ − && ′

loss ′ ≤HRR)qqf( b

* (74) 

38
Equation 74 states that (analogous to HRR) there is a critical value of ηc below which flame 

extinction will occur in a flammability test. 

)qq(f

*HRR

flame loss

b

c ′′ − ′′ ≤η && (75) 

Figure 1 showed generic ηc and flame resistance results for commercial polymers. Figure 20 

shows grouped ratings for 50 polymers in the UL V and UL H tests for flammability of plastics 

[27] (section 5.4 and table 8). Three ranges of flammability are observed with respect to ηc in 

figures 1 and 20: (1) no ignition in a vertical test (UL 94 V0 rating or better) for 

ηc < 200 kJ/kg-K, (2) self-extinguishing (UL 94 V) behavior after 10-30 seconds of burning in a 

vertical test for ηc = 200-400 kJ/kg-K, and (3) a self-propagating flame in a horizontal burning 

test for ηc > 400 kJ/kg-K. 

10 100 1000 10,000

HB

V2

V1

V0

Heat Release Capacity (ηc), J/g-K

UL 94 

Rating Halogen containing

 Flammability

FIGURE 20. FLAMMABILITY RATING IN UL 94 TEST VERSUS HEAT RELEASE 

CAPACITY OF 50 POLYMERS 

TABLE 8. UL 94 20-mm VERTICAL BURNING TEST CLASSIFICATION CRITERIA 

Classification 

Observation V-0 V-1 V-2 

t1 or t2 for any specimen 10 s 30 s 30 s 

t1 + t2 for 5 specimens 50 s 250 s 250 s 

t2 + t3 for any specimen 30 s 60 s 60 s 

Afterflame or afterglow up to clamp, any specimen No No No 

Ignition of cotton No No Yes 

39
With regard to flammability as measured in the LOI test [25] (section 5.5.1), if equation 52 

applies and (extinction) = φ LOI, then equation 74 gives the criterion for flame extinction 

in the LOI test. 

qflame & ′′

)qLOIf(

*HRR

η

loss

b c − ′′ ≤

φ & (76) 

Equation 76 suggests that LOI and ηc are inversely related. Figure 21 shows a plot of generic 

values of LOI versus ηc (see table A-6 in appendix A). A power law, LOI = 125/ , can be fit 

to the data with reasonable accuracy (correlation coefficient = 0.84), confirming the inverse 

relationship between LOI and η

ηc

1/4

c suggested by equation 76. 

0 

20 

40 

60 

80 

100 

10 100 1000 

Limiting Oxygen Index (LOI), [O2], % v/v 

Heat Release Capacity (ηc), J/g-K 

10,000 

LOI = 

125 

Halogen containing 

η 1/4 

c 

FIGURE 21. LIMITING OXYGEN INDEX VERSUS HEAT RELEASE CAPACITY 

FOR 50 POLYMERS 

4.8 SMOKE.

The smoke extinction area (SEA, m2

/kg) is a global measure of the condensed phase (liquid and 

solid) products of flaming combustion, having units of square meters of particulate scattering 

surface per kilogram of material burned. The SEA is measured in a fire calorimeter under wellventilated conditions from optical extinction of the combustion gas stream [25]. Appendix A, 

table A-7 lists the specific SEA for a variety of polymers averaged from the literature. Figure 22 

shows a plot of SEA data in table A-7 versus the flaming combustion efficiency of the same 

polymer listed in table A-5. It is seen that SEA varies by a factor of 100 between different 

polymers and is particularly sensitive to combustion efficiency in the range χ = 0.8-1.0. Below 

χ = 0.8, SEA is essentially independent of combustion efficiency. 

40
The effect of chemical structure on smoke production can generally be described as follows. 

Aliphatic oxygenated fuels (POM, PMMA, and PA) and those with high thermal stability (PBI, 

PAI, PEI, PES, PEEK, and Polyarylsulfone) or an extremely low burning rate 

(polytetrafluoroethylene, chlorinated polyvinylchloride, and wood) tend to produce less smoke 

per unit mass of material burned than aliphatic (PE and PP), aromatic oxygen- and nitrogencontaining (PET, PBT, epoxy (EP), PC, polyurethane (PU), bismaleimide, VE, and PPO) or 

aromatic sulfur-containing (PSU and PPS) polymers. 

10

100

1,000

10,000

0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1

Smoke Extinction Area (SEA), m2/kg

Combustion Efficiency (χ)

Halogen containing

FIGURE 22. SMOKE EXTINCTION AREA VERSUS FLAMING COMBUSTION 

EFFICIENCY (χ) FOR 40 POLYMERS 

Polymers with low thermal stability and pendant (acrylonitrile-butadiene-styrene terpolymer 

(ABS) and PS) or backbone (EP, unsaturated polyester thermoset (UPT), VE, and PPO) aromatic 

groups produce a large amount of smoke because their thermal degradation products (fuel gases) 

contain the aromatic nucleus for soot formation (see section 2.1). 

Low thermal stability aromatic polymers with high SEA (ABS, EP, and PS) produce 50% more 

smoke per unit mass when brominated flame-retardants are added to inhibit combustion. These 

materials, listed at the bottom of table A-7 in appendix A, produce 5-20 times more smoke per 

unit mass than the commodity and engineering polymers in the top half of the table. Silicones 

are anomalous with respect to SEA because the scattering particles are silica (SiO2), which is a 

complete (rather than incomplete) combustion product of the backbone silicon. 

The highest SEAs are associated with halogen-containing polymers (rigid and flexible PVC and 

PMMA/PVC alloy) apparently because of combustion inhibition by chlorine (see equations 1-3 

and figure 22). 

41
The smoke point is another measure of the tendency of a fuel to produce smoke and this quantity, 

like smoke extinction area, is related to the chemical composition and structure of the fuel. The 

smoke point is defined as the minimum fuel mass flow rate at which smoke first escapes from 

the tip of a laminar diffusion flame (see figure 2), i.e., the residence time of the smoke in the 

combustion zone becomes too short to effect complete oxidation. The results of the smoke point 

test are qualitatively similar to the SEA data in table A-7 with respect to chemical structure and 

smoke-forming tendency. In particular, it was found that the smoke-forming tendency, as 

determined by smoke point measurements, was lowest for oxygenated fuels (alcohols, aldehydes, 

esters, and ethers) and increases through the series—alkanes, branched alkanes, alkenes, and 

aromatics. 

5. FIRE AND FLAMMABILITY TESTS. 

5.1 TERMINOLOGY: FIRE VERSUS FLAMMABILITY. 

There is no universal agreement on the definition of flammability tests and how they are 

different from fire tests. A common application of fire and flammability tests is to obtain data 

for regulatory compliance, as will be discussed in the next section. Fire safety codes and 

regulations are generally based on two strategies. The first strategy involves preventing or, at 

least, minimizing the likelihood of ignition. Since, in practice, it is not possible to completely 

eliminate ignition, the second strategy involves managing the impact of a subsequent fire. 

Flammability tests are typically associated with the first strategy. A small specimen (linear 

dimensions of the order of centimeters or inches) of a polymer is exposed to a small heat source 

(Bunsen burner type flame, hot wire, etc.) for a short duration (seconds). Pass/fail criteria are 

based on ignition of the specimen during exposure, formation of flaming droplets or sustained 

flaming or smoldering after removal of the heat source. 

For the purpose of this report, fire tests are associated with the second strategy and defined as 

experimental methods to characterize the behavior of polymers under more severe thermal 

exposure conditions that are representative of the growth phase of a cargo compartment fire. 

These conditions are simulated with a gas-fired or electrical heater or a large gas burner turbulent 

diffusion flame (flame length of the order of a meter or several feet). The incident heat flux to 

the specimen is primarily radiative when heaters are used and mainly convective for flame 

exposure. Total incident heat flux varies from approximately 1 kW/m2

 to more than 100 kW/m2. 

Note that the maximum radiant heat flux from the sun on earth is approximately 1 kW/m2

. 

Polymers that are not treated with fire-retardant chemicals typically ignite when exposed to heat 

fluxes of 10-20 kW/m2

 in the presence of a small pilot flame or hot spark. 

The aforementioned definitions imply that flammability tests are concerned with a lower level of 

performance. Passing a flammability tests does not mean that a material will be less hazardous 

when involved in a fire. This is consistent with one definition of the term flammable, which is 

described in ASTM E 176, “Terminology of Fire Standards,” as “subject to easy ignition and 

rapid flaming combustion” [25]. 

The characteristics that are measured in a fire test are indicative of the performance of the 

material under the conditions of the test and are, therefore, referred to as fire-test-response 

42
characteristics. They may or may not be indicative of the hazard of a material under actual fire 

conditions. The most common fire-test-response characteristics that are measured in fire tests 

are the ease of ignition, flame spread, heat release, smoke generation, and toxic potency of 

smoke [20 and 25]. 

5.2 FIRE AND FLAMMABILITY TEST APPLICATIONS. 

There are three distinct applications of fire and flammability tests, which are discussed below. 

5.2.1 Regulatory Compliance. 

Codes and regulations have been developed in many countries to ensure a level of public fire 

safety that is acceptable to society. The main objectives of these codes and regulations in terms 

of fire and flammability of materials are to limit the likelihood of ignition and to reduce the rate 

of fire growth to the critical stage of flashover in the compartment of fire origin. In addition, 

codes and regulations also limit the quantities of particulate matter (affects visibility) and of 

toxic and corrosive products of combustion that can cause human casualties and excessive 

damage to equipment. 

Codes and regulations are intended to provide a minimum level of safety based on loss 

objectives that are acceptable to society. Other stakeholders often specify additional 

requirements. For example, an insurance company might have more stringent requirements to 

reduce the risk of incurring excessive losses in the event of a fire. Building owners and operators 

might require a level of safety that exceeds the building code. Manufacturers of transportation 

vehicles might issue specifications for their product suppliers that go beyond the regulations. 

Codes, regulations, and specifications specify acceptance criteria for the products that are used in 

specific areas of the environment that is regulated. These criteria are based on performance in 

one or more fire or flammability tests. This approach has been applied extensively to two 

environments where the potential exists for large life loss: buildings and transportation vehicles. 

Some important fire and flammability tests that are used in different parts of the world to ensure 

a specific level of safety in these two environments are summarized in the following sections. 

5.2.2 Quality Assurance and Research. 

Fire and flammability tests are also used in support of production control. The objective of a 

production control program is to ensure that a product which is sold in the marketplace is 

identical to the specimen that was originally tested for regulatory compliance. Often, it is not 

practical or economically feasible to use the qualification test(s) in a follow-up production 

control program, and a simple test is often adequate to verify the consistency of the product. 

Relatively simple flammability tests are, therefore, most often used for the purpose of quality 

assurance. The same tests are then used in research and development of new products. 

5.2.3 Data for Fire Safety Engineering Design and Analysis. 

Fire safety codes and regulations are largely prescriptive. This means that they contain 

acceptance criteria for materials, products, and assemblies based on performance in one or 

43
several tests. The overall level of safety that is accomplished is not explicitly stated. Sometimes 

it is not possible to demonstrate that a material, product, or assembly meets the specified 

acceptance criteria. For example, it might not be possible to obtain a valid test result for a 

product that melts and shrinks away from the heat source in a fire test. Fire safety codes and 

regulations generally contain a clause that gives the enforcing official the authority to accept a 

variance from the specified acceptance criteria. To persuade the enforcing official, it is 

necessary to demonstrate that the material, product, or assembly does not compromise the level 

of safety that is implicit in the code or regulation. This usually requires an engineering analysis 

and tests to obtain material properties that are needed in support of the analysis. 

In recent years, performance-based codes and regulations have become increasingly popular. 

Such codes and regulations explicitly state the minimum level of performance of the system 

(building, railcar, etc.) in case of fire. That a particular design meets the specified level of 

performance is again based on an engineering analysis. Similar analyses are performed in 

support of the investigation and reconstruction of actual fire incidents. 

5.3 FIRE AND FLAMMABILITY TEST STANDARDS. 

Regardless of the application, it is important that fire and flammability test methods be free of 

systematic error (bias). It is also essential that consistent results can be obtained from 

experiments repeated at different times within one laboratory (repeatability) and that there is 

reasonable agreement between the results for the same material, product, or assembly tested in 

different laboratories (reproducibility). Those are the reasons why fire safety codes, regulations, 

and specifications refer to standardized fire and flammability test methods and why test data 

needed in support of fire engineering are obtained with standardized experimental protocols. 

5.3.1 Consensus-Based Test Standards. 

Most fire and flammability test standards are developed by consensus-based committees. The 

rules and procedures by which these committees operate ensure that the development cannot be 

dominated by a single interest group and that there is reasonable agreement between the different 

interest groups represented on the committee. 

ASTM International (previously the American Society for Testing and Materials) and the 

National Fire Protection Association (NFPA) are the primary consensus-based organizations in 

the U.S. that develop and maintain fire and flammability test standards. Committee E05 on Fire 

Tests is the primary committee in ASTM that develops fire and flammability test standards [25]. 

Several material or product-oriented committees have subcommittees that develop fire and 

flammability test standards as well. For example, committee D20 on Plastics has a 

subcommittee on thermal properties (D20.30) that develops and maintains some fire and 

flammability test standards for plastics. The Fire Test Committee is responsible for all fire and 

flammability test standards that are used by any of the fire safety codes and standards published 

by NFPA. A number of test laboratories in the U.S., such as UL and FM Global, have 

established a consensus process that meets the requirements of the American National Standards 

Institute so that they now can publish American National Standards. 

44
International fire and flammability test standards are developed by the International Organization 

for Standardization (ISO) and the International Electrotechnical Committee (IEC). The latter is 

concerned with electrical products only. Technical committees TC 92 and TC 89 are the primary 

committees that develop and maintain fire and flammability test standards in ISO and IEC 

respectively. As in ASTM, there are a number of product or industry-specific committees in ISO 

that also develop fire and flammability test standards. For example, SC1 on Test Methods of 

ISO TC 136 on Furniture has published two ignition tests for upholstered seating. An important 

difference between ISO and IEC versus ASTM and NFPA is that the international committees 

establish consensus on a geographical basis. Each country that actively participates in the work 

can be a voting member on an ISO or IEC committee. Committees are composed in a similar 

manner in CEN and CENELEC, which are the European counterparts of ISO and IEC 

respectively. However, member countries can have multiple votes in CEN and CENELEC 

committees. The number of votes is a function of the population of the country. 

5.3.2 Other Types of Test Standards. 

There are many fire and flammability tests methods that are not developed by a consensus-based 

process. In the U.S. these types of test standards are typically promulgated by regional or federal 

government agencies. The latter are published as part of the regulations that refer to these test 

methods in the Code of Federal Regulations (CFR), although many federal regulations rely on 

consensus-based test standards. Some federal fire and flammability test standards are also 

described in military specifications (MIL specs) issued by the different agencies of the 

Department of Defense. The U.S. government has recognized the advantages of using test 

standards that have been subjected to a review and are accepted by all interest groups and is now 

actively supporting the adoption of consensus-based tests standards. Examples of regional fire 

and flammability test standards that are not consensus-based are the California Technical 

Bulletins to assess the fire and flammability characteristics of upholstered furniture and 

mattresses. Finally, specifications for suppliers issued by manufacturers of passenger airplanes, 

railcars, etc., might also rely on fire and flammability test procedures that have not been 

developed by a consensus-based process. For example, Airbus, Boeing, and Bombardier all have 

their own fire and flammability test standards. 

5.4 TESTING FOR REGULATORY COMPLIANCE. 

There are literally hundreds of fire and flammability tests for polymers [5 and 25]; therefore, it is 

not possible to provide an overview of these tests in this report. A few important tests have been 

selected to illustrate the key concepts. These tests include the ones that are referred to in the first 

four sections of this report: the UL 94 20-mm Vertical Burning Test [27], the Limiting Oxygen 

Index Test [25], the Cone Calorimeter [25], and the Pyrolysis Combustion Flow Calorimeter [29]. 

For guidance on available fire and flammability test methods to evaluate polymers, the reader is 

referred to ASTM D 3814, “Standard Guide for Locating Combustion Test Methods for 

Polymeric Materials” [25]. A comprehensive review of fire and flammability tests used in 

support of codes and regulations in different parts of the world can be found in Troitzsch [5]. 

45
5.4.1 Typical Example of a Flammability Test. 

The UL 94 standard provides procedures for bench-scale tests to determine the acceptability of 

plastic materials for use in appliances or other devices with respect to flammability under 

controlled laboratory conditions. The standard includes several test methods that are employed 

depending upon the intended end-use of the material and its orientation in the device. The 

standard outlines two horizontal burning tests, three vertical burning tests, and a radiant panel 

flame spread test. The most commonly used method is summarized below as a typical example 

of a flammability test. 

The first vertical burning test described in the UL 94 standard is the 20-mm Vertical Burning 

Test; V-0, V-1, or V-2. The UL 94 test cabinet is shown in figure 23. The V-0, V-1, or V-2 

classification is based on the duration of afterflaming or afterglowing following the removal of 

the burner flame, as well as the ignition of cotton by dripping particles from the test specimen. 

Photo Courtesy of Fire Testing Technology ©2004 

FIGURE 23. UL 94 CABINET 

In this test, specimens measuring 125 mm in length by 13 mm wide are suspended vertically and 

clamped at the top end. A thin layer of cotton is positioned 300 mm below the test specimen to 

catch any molten material that may drop from the specimen. A 20-mm-long flame from a 

methane burner is applied to the center point on the bottom end of the specimen. The burner is 

positioned such that the burner barrel is located 10 mm below the bottom end of the material 

specimen. The flame is maintained for 10 seconds, and then removed to a distance of at least 

150 mm. Upon flame removal, the specimen is observed for afterflaming and its duration time 

recorded (t1). As soon as the afterflame ceases, the burner flame is reapplied for an additional 

10 seconds, then removed again. The duration of afterflaming (t2) or afterglowing (t3) are noted. 

Based on the results, the material is classified as either V-0, V-1, or V-2, based on the criteria 

outlined in table 8. 

46
5.4.2 Typical Examples of Fire Tests. 

The following two examples are commonly used tests that illustrate two distinct approaches to 

simulate the thermal exposure conditions in a preflashover compartment fire. The Steiner 

Tunnel Test uses a gas burner to heat the specimen, primarily by convection. The Radiant 

Flooring Panel test relies on a gas-fired panel that exposes a flooring specimen to a radiant heat 

flux profile. 

5.4.2.1 The Steiner Tunnel Test. 

The primary intent of the Steiner Tunnel Test is to quantify the wind-aided flame spread 

propensity of the material tested. It is the most common reaction-to-fire test method prescribed 

by U.S. model building codes. The Steiner Tunnel Test is described in ASTM E 84, “Standard 

Test Method for Surface Burning Characteristics of Building Materials,” and NFPA 255, 

“Standard Method of Test of Surface Burning Characteristics of Building Materials.” The 

apparatus, as shown in figure 24, consists of a long tunnel-like enclosure measuring 8.7 by 0.45 

by 0.31 m. The test specimen is 7.6 m long and 0.51 m wide and is mounted in the ceiling 

position. It is exposed at one end, designated as the burner end, to a 79-kW gas burner. There is 

a forced draft through the tunnel from the burner end with an average initial air velocity of 

1.2 m/s. A smoke photometer is mounted on the exhaust duct. The photometer consists of a 

white light source on one side of the duct and a photocell on the opposite side of the duct. 

Photo Courtesy of Southwest Research Institute ©2004 

FIGURE 24. THE STEINER TUNNEL TEST APPARATUS 

The test measurements consist of flame spread over the surface and light absorption in the 

exhaust duct of the tunnel. The test duration is 10 minutes. A flame spread index (FSI) is 

calculated on the basis of the area under the curve of flame tip location versus time. The FSI is 0 

for an inert board and is normalized to approximately 100 for red oak flooring. The smokedeveloped index (SDI) is equal to 100 times the ratio of the area under the curve of light 

absorption versus time for the 10-minute test duration to the area under the curve for red oak 

flooring. Thus, the SDI of red oak flooring is 100, by definition. 

47
The classification of linings in the model building codes in the U.S. is based on the FSI. There 

are three classifications: Class A, or I, for products with FSI ≤ 25; Class B, or II, for products 

with 25 < FSI ≤ 75; and Class C, or III, for products with 75 <FSI ≤200. Class A, or I, products 

are generally permitted in stairways. Class B, or II, products can be used in corridors, and Class 

C, or III, products are allowed in other rooms and areas. The model building codes do not permit 

interior finishes that produce excessive amounts of light-obscuring smoke. Products that have to 

be tested according to the tunnel test must have an SDI of 450 or less. 

5.4.2.2 The Radiant Flooring Panel Test. 

The National Bureau of Standards (NBS, currently the National Institute of Standards and 

Technology) conducted a series of full-scale fire tests in the 1970s to investigate the fire hazard of 

floor coverings. The main concern was flame spread from a fire room to a connected corridor. 

This work resulted in the development of the Radiant Flooring Panel Test. This test is described 

in ASTM E 648, “Standard Test Method for Critical Radiant Flux of Floor Covering Systems 

Using a Radiant Heat Energy Source” and NFPA 253, “Standard Method of Test for Critical 

Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source.” The 

international version of this test method, ISO 9239-1 “Reaction to Fire Tests for Floor 

Coverings—Determination of the Burning Behavior Using a Radiant Heat Source,” includes a 

photometer in the exhaust stack to measure smoke optical density (see figure 25). 

Photo Courtesy of Fire Testing Technology ©2004 

FIGURE 25. THE RADIANT FLOORING PANEL TEST APPARATUS 

The Radiant Flooring Panel Test apparatus consists of an air-gas-fueled radiant heat panel 

inclined at 30 degrees to and directed at a horizontally mounted floor covering system specimen. 

The radiant panel generates a heat flux distribution along the 1-m length of the test specimen 

48
from a nominal maximum of 10 kW/m2

 (1 W/cm2) to a minimum of 1 kW/m2 (0.1 W/cm2). The 

test is initiated by open-flame ignition from a pilot burner. The heat flux at the location of 

maximum flame propagation is reported as the critical radiant flux. 

5.4.2.3 Rate of Heat Release Test for Aircraft Cabin Materials. 

The Federal Aviation Administration requires (14 CFR 25.853) that large areas, including 

interior ceiling and wall panels, partitions, galley structures, cabinets, and stowage compartments 

of commercial transport aircraft, pass a rate of heat release test in addition to flammability and 

smoke tests. The rate of heat release apparatus (see figure 26) is a modified version of the 

ASTM E-906, “Standard Test Method for Heat and Visible Smoke Release Rates of Materials 

and Products” (configuration A). Samples are 150- by 150-mm square and are cut from cabin 

components or tested in representative thickness. Samples are exposed to a radiant heat flux of 

35 kW/m2

 in a vertical orientation and ignited by an impinging pilot flame. The rate of heat 

released by flaming combustion is deduced from the calibrated temperature rise of the air stream 

passing over the sample surface at a prescribed flow rate. The maximum rate of heat release 

cannot be greater than 65 kW/m2

 over the entire duration of the 5-minute test, and the heat 

released during the first 2 minutes of the test cannot be greater than 65 kW-min/m2

. 

Photo Courtesy The Govmark Organization, Inc. 

FIGURE 26. RATE OF HEAT RELEASE APPARATUS 

49
5.5 TESTING FOR QUALITY ASSURANCE AND RESEARCH. 

5.5.1 The LOI Test. 

The LOI test is a typical example of a method that is used to control the production of materials, 

products, and assemblies and in research to develop new products. This test is standardized in 

North America as ASTM D 2863, “Standard Test Method for Measuring the Minimum Oxygen 

Concentration to Support the Candle-Like Combustion of Plastics (Oxygen Index),” and 

internationally as ISO 4589-2, “Plastics—Determination of Burning Behavior by Oxygen 

Index—Part 2: Ambient-Temperature Test.” The test does not correlate well with other fire and 

flammability tests nor does it provide a reliable indication of material performance in real fires. 

However, the results appear to be very sensitive to the composition of the material and the test is, 

therefore, ideally suited to serve as a quality assurance tool of fire-retardant-treated materials. 

The LOI test apparatus consists of a glass tube 75 to 100 mm in diameter and 450 to 500 mm in 

height and is shown in figure 27. A specimen with a height between 70 and 200 mm and a width 

of 10 to 20 mm is supported inside the glass tube. A gas mixture of oxygen and nitrogen is 

supplied at the bottom of the tube and a small candle-like flame is applied to the top of the 

specimen in an attempt to ignite it. The objective is to find the minimum oxygen concentration 

in nitrogen that will result in sustained combustion for at least 3 minutes or excessive flame 

propagation down the specimen. The dimensions of the specimen and the limit of excessive 

flame propagation depend on the type of material that is being tested. 

Photo Courtesy of Fire Testing Technology ©2004 

FIGURE 27. THE LOI TEST APPARATUS 

50
5.5.2 The Pyrolysis Combustion Flow Calorimeter. 

The pyrolysis combustion flow calorimetry (PCFC) is a method for measuring quantitative 

flammability parameters of combustible materials and is used in research to develop new 

polymers with improved fire performance (Lyon and Walters 2004). In PCFC, the condensedphase and gas-phase processes of flaming combustion are separately reproduced through 

controlled pyrolysis of milligram samples in an inert gas stream and high-temperature thermal 

oxidation (combustion) of the pyrolyzate in excess oxygen. The rate of heat released by 

combustion per unit mass of sample during the test (specific HRR, section 4.6) is measured by 

oxygen consumption calorimetry (section 4.2). Time-integration of the specific HRR gives the 

net heat of combustion of the fuel gases h . The maximum value of the specific HRR, 

normalized for the sample heating rate, is a material flammability parameter with the units and 

significance of a heat (release) capacity that is a good predictor of flame test results and fire 

performance. The temperature at maximum specific HRR is a good approximation of the 

ignition temperature (see sections 3.1, 4.4, and table A-1). 

c

0

5.6 TESTING TO OBTAIN ENGINEERING DATA. 

HRR is the primary characteristic to quantify the fire hazard of a material. Most fire tests to 

obtain engineering data, therefore, measure HRR. The rate of heat release is generally 

determined using oxygen consumption calorimetry. For a large number of organic liquids and 

gases [20], a nearly constant net amount of heat is released per unit mass of oxygen consumed 

for complete combustion. Sixty years later, researchers at NBS found this to also be true for 

organic solids and obtained an average value for this constant of 13.1 MJ/kg of O2. This value 

may be used for practical applications and is accurate with very few exceptions to within ±5%. 

Thornton’s rule implies that it is sufficient to measure the oxygen consumed in a combustion 

system to determine the net heat released. This method, generally referred to as oxygen 

consumption calorimetry, is now the most widely used and accurate method for measuring HRR 

in experimental fires. A summary of the most commonly used oxygen consumption calorimeters 

follows. 

5.6.1 Bench-Scale Calorimeters. 

5.6.1.1 The Cone Calorimeter. 

The Cone Calorimeter is standardized in North America as ASTM E 1354, “Test Method for 

Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen 

Consumption Calorimeter,” and internationally as ISO 5660-1, “Fire Tests – Reaction to Fire – 

Part 1: Rate of Heat Release From Building Products (Cone Calorimeter Method).” A 

commercial version of the Cone Calorimeter is shown in figure 28. 

A 100- by 100-mm square sample is exposed to the radiant flux of an electric heater. The heater 

has the shape of a truncated cone (hence the name of the instrument) and is capable of providing 

heat fluxes to the specimen up to 100 kW/m2

. An electric spark plug is used for the piloted 

ignition. The heater temperature is measured as an average of the readings from three 

thermocouples that are in contact with the coil. It is set and maintained at a certain level by a 

three-term controller. Calibration of heat flux as a function of heater temperature is performed 

51
with a Schmidt-Boelter type total heat flux meter. Prior to testing, the heater temperature is set 

at the appropriate value, resulting in the desired heat flux. 

Photo Courtesy of Fire Testing Technology ©2004 

FIGURE 28. COMMERCIAL VERSION OF THE CONE CALORIMETER 

At the start of a test, the specimen in the appropriate holder is placed on the load cell, which is 

located below the heater. The load cell has a tare adjustment. This allows for a mechanical shift 

of the zero so that high accuracy mass loss measurements can be made, even if the mass of the 

holder and a possible substrate are much higher than the specimen. As soon as the pyrolysis 

products released by the specimen ignite, the electric spark plug is removed. All combustion 

products and entrained air are collected in the hood. An orifice plate at the entrance of the 

exhaust duct results in an almost uniform gas mixture. At a sufficient distance downstream from 

the mixing orifice, a gas sample is taken and analyzed for O2. A laser photometer is located 

close to the gas-sampling point to measure light extinction by the smoke. The exhaust gases are 

removed by a high-temperature blower. The flow rate can be adjusted between 0 and 50 liters 

per second. For standard testing, the Cone Calorimeter is used in constant volume mode and the 

fan speed is set at 24 liters per second. Downstream of the fan is a second orifice plate. 

Measurements of the differential pressure across and gas temperature at the orifice plate are used 

for calculating the mass flow of the exhaust gases. 

52
The Cone Calorimeter can also be used to obtain other data in support of fire safety engineering 

analysis. For example, the instrument can be used to determine ignition characteristics of a 

material by measuring the time to ignition at different heat flux levels. A laser smoke 

photometer is mounted on the duct to determine the smoke production rate. A continuous gas 

sample can be taken from the exhaust duct and analyzed to determine the concentration of 

different toxic and corrosive products of combustion in the effluents. Fourier Transform Infrared 

Spectroscopy is now a common method to measure the concentration of toxic and irritant gases 

in the exhaust duct of the Cone Calorimeter. 

5.6.1.2 The Fire Propagation Apparatus. 

The Fire Propagation Apparatus was developed by FM Global Research (previously Factory 

Mutual Research Corporation). The test is described in ASTM E 2058, “Standard Test Methods 

for Measurement of Synthetic Polymer Material Flammability Using a Fire Propagation 

Apparatus (FPA).” A commercial version of the Fire Propagation Apparatus is shown in 

figure 29. 

Photo Courtesy of Fire Testing Technology ©2004

FIGURE 29. COMMERCIAL VERSION OF THE FIRE PROPAGATION APPARATUS 

The Fire Propagation Apparatus is similar to the Cone Calorimeter and can be used to obtain the 

same types of measurements. However, there are some significant differences that are briefly 

summarized below. 

• The products of pyrolysis are ignited with a small hydrogen flame that is located 10 mm 

above the center of the specimen. 

53
• The specimen is surrounded by a quartz tube. This makes it possible to conduct tests in a 

vitiated or oxygen-enriched atmosphere. The tube allows for a forced flow over the 

specimen surface and reduces the effect of external heat flux and specimen surface 

temperature on convective heat losses prior to ignition. 

• Specimens are heated by high-temperature (approximately 2300 K) tungsten filament 

lamps that are located outside the quartz tube. Since the spectral response of many 

materials is different for a radiant heat source at this temperature compared to heat fluxes 

in fires from sources at much lower temperatures, specimens have to be blackened. In 

addition, due to the type of heaters that are used and the quartz tube arrangement, the 

maximum incident heat flux that can be obtained is 70 kW/m2

. 

5.6.2 Large-Scale Calorimeters. 

5.6.2.1 The Room/Corner Test. 

The Room/Corner Test is used to evaluate the fire growth characteristics of wall and ceiling 

linings. The walls and ceiling of a 2.4- by 3.6- by 2.4-m room are lined with the test material. A 

gas burner is placed in one of the rear corners of the room opposite the 0.8- by 2.0-m open 

doorway in the front wall. Products of combustion are collected in a hood located in front above 

the door opening and extracted by a high-temperature blower through the exhaust duct. The 

instrumentation in the exhaust duct is similar to that in the Cone Calorimeter, except the flow 

rate is typically determined on the basis of bidirectional probe measurements of centerline 

velocity and the smoke photometer often uses a white light source instead of a He-Ne laser. 

Several Room/Corner Test standards have been developed and are used for regulatory purposes. 

For example, NFPA 265, “Standard Methods of Fire Tests for Evaluating Room Fire Growth 

Contribution of Textile Wall Coverings,” is required in the U.S. to qualify textile wall coverings 

for use in unsprinklered spaces of certain types of buildings. ISO 9705, “Fire Tests – Full-Scale 

Room Test for Surface Products,” is more severe than NFPA 265 and is used to qualify materials 

as fire restricting for high-speed craft (small passenger ferries operating within a short distance 

from shore). Figure 30 shows an ISO 9705 test in progress. 

5.6.2.2 The Furniture Calorimeter. 

Often, it is very difficult to determine the burning behavior of complex objects on the basis of the 

fire performance of its individual components. For example, it is very hard to determine the 

burning behavior of upholstered furniture on the basis of the fire characteristics of the foam, 

fabric, and framing materials and to account for the geometry and configuration of the furniture 

and how it is ignited. It is much more practical to measure the HRR and related properties for 

the complete object. This can be done in a furniture calorimeter. The object is placed on a load 

platform to measure the mass loss rate during the test. It is ignited with a standardized ignition 

source and the products of combustion are collected in a hood and extracted through an exhaust 

duct. Measurements of oxygen concentration, flow rate, and light transmission in the exhaust 

duct are used to determine the HRR and smoke production rate from the object as a function of 

time. Furniture calorimeter test standards have been developed in ASTM for chairs, mattresses, 

and stacked chairs. The corresponding designations are ASTM E 1537, ASTM E 1590, and 

ASTM E 1822 respectively. 

54
Photo Courtesy of Southwest Research Institute ©2004 

FIGURE 30. ISO 9705 ROOM/CORNER TEST IN PROGRESS 

5.6.2.3 The Intermediate-Scale Calorimeter. 

One of the limitations of the Cone Calorimeter is that only relatively small samples can be 

evaluated. As a result, products that have joints or layered materials with a thickness exceeding 

50 mm can generally not be tested in the Cone Calorimeter in a representative manner. For those 

types of products or assemblies, a larger calorimeter is required. Such an intermediate-scale 

calorimeter forms the subject of ASTM E 1623, “Standard Test Method for Determination of 

Fire and Thermal Parameters of Materials, Products, and Systems Using an Intermediate Scale 

Calorimeter (ICAL).” 

The ICAL apparatus consists of an array of gas heaters, forming a vertical radiant panel with a 

height of approximately 1.33 m and width of approximately 1.54 m. The test specimen measures 

1 by 1 m and is positioned parallel to the radiant panel. The heat flux to the specimen is preset to 

a maximum of 60 kW/m2

 by adjusting the distance to the panel. Gas flow to the panel is 

controlled to maintain the temperature to the panel, and consequently, the heat flux to the 

specimen. The products of pyrolysis from the specimen are ignited with hot wires located close 

to, but not in contact with, the specimen at its top and bottom. The specimen is placed in a 

holder that is put on a load cell to measure mass loss during testing. The panel and specimen are 

positioned beneath the hood of the standard ISO 9705 room/corner test. All products of 

combustion are collected in the hood and continuously extracted through the exhaust duct. 

Instrumentation is provided in the duct for measuring HRR on the basis of oxygen consumption. 

A smoke photometer is also included for measuring smoke obscuration in the duct. 

55
5.6.2.4 The Fire Products Collector. 

The first industrial-size calorimeter for fires into the megawatt (MW) range was built at Factory 

Mutual (currently FM Global) around 1980. This calorimeter, also referred to as the FM Fire 

Products Collector, was designed to measure heat and other fire products from test fires up to a 

size associated with sprinkler activation in commodity warehouse storage and other 

representative occupancies. Approximately 10 years later, a similar industrial-size calorimeter 

for HRR measurements up to 10 MW was constructed at SP National Testing Laboratory in 

Sweden. Since then several other laboratories, such as the National Research Council of Canada, 

the Fire Research Station in the UK, Underwriters Laboratories and Southwest Research Institute 

in the U.S. developed the capability of measuring HRR from large fires into the MW range. 

6. REFERENCES. 

1. C.J. Hilado, Flammability Handbook for Plastics, 5th edition, Technomic Publishing Co., 

Lancaster, Pennsylvania, 1998. 

2. A.H. Landrock, Handbook of Plastics Flammability and Combustion Toxicology, Noyes 

Publications, Park Ridge, NJ, 1983. 

3. F.L. Fire, Combustibility of Plastics, Van Nostrand Reinhold, New York, 1991. 

4. C.A. Harper, ed., Handbook of Building Materials for Fire Protection, McGraw-Hill, 

New York, NY, 2004. 

5. Jürgen Troitzsch, Plastics Flammability Handbook, Hanser Publishers, Munich, 2004. 

6. M.Le Bras, G. Camino, S. Bourbigot, and R. Delobel, Fire Retardancy of Polymers: The 

Use of Intumescence, The Royal Society of Chemistry, Cambridge, UK, 1998. 

7. A.R. Horrocks and D. Price, eds., Fire Retardant Materials, Woodhead Publishing, Ltd., 

Cambridge, England, 2001. 

8. G.L. Nelson, ed. Fire and Polymers: Hazards Identification and Prevention, ACS 

Symposium Series 425, American Chemical Society, Washington, D.C., 1990. 

9. G.L. Nelson, ed., Fire and Polymers II: Materials and Tests for Hazard Prevention, ACS 

Symposium Series 599, American Chemical Society, Washington, D.C., 1995. 

10. A.F Grand and C.A. Wilkie, eds., Fire Retardancy of Polymeric Materials, Marcel 

Dekker, Inc., NY, 2000. 

11. The SFPE Handbook of Fire Protection Engineering, 3rd edition, Boston, MA, Society 

of Fire Protection Engineers, 2002. 

12. D.D. Drysdale, An Introduction to Fire Dynamics, 2nd edition, John Wiley & Sons, New 

York, 1998. 

56
13. G. Cox, ed., Combustion Fundamentals of Fire, Academic Press, Harcourt Brace & Co., 

Publishers, London UK, 1995. 

14. R. Friedman, Principles of Fire Protection Chemistry and Physics, National Fire 

Protection Association, Quincy, MA, 1998. 

15. C.F. Cullis and M.M. Hirschler, The Combustion of Organic Polymers, Clarendon Press, 

Oxford, England, 1981. 

16. G. Pal and H. Macskasy, Plastics: Their Behavior in Fires, Elsevier, New York, 1991. 

17. R.A. Strehlow, Combustion Fundamentals, McGraw-Hill, New York, 1984. 

18. R. Turns, An Introduction to Combustion– Concepts and Applications, McGraw-Hill, 

New York, 1996. 

19. I. Glassman, Combustion, 3rd ed., Academic Press, New York, 1996. 

20. V. Babrauskas and S.J. Grayson, eds., Heat Release in Fires, Elsevier Applied Science, 

London, UK, 1992. 

21. J.G. Quintiere, Principles of Fire Behavior, Del Mar Publishers, Albany, NY, 1998. 

22. D.W. Van Krevelen, Properties of Polymers, 3rd ed., Elsevier Scientific, New York, 

1990. 

23. J.R. Hallman, “Ignition Characteristics of Plastics and Rubber,” Ph.D. Thesis, the 

University of Oklahoma, 1971. 

24. V. Babrauskas, Ignition Handbook, Fire Science Publishers, Issaquah, WA, 2003. 

25. ASTM Fire Test Standards, Fifth Edition, American Society for Testing and Materials, 

West Conshohocken, PA, 1999. 

26. R.E. Lyon and R.N. Walters, “Pyrolysis Combustion Flow Calorimetry,” Journal of 

Analytical and Applied Pyrolysis, 71, 27-46 (2004) 

27. Flammability of Plastic Materials, Northbrook, IL: Underwriters Laboratories Inc., UL 

94 Section 2 (Horizontal: HB) and Section 3 (Vertical: V-0/1/2) 1991. 

28. J. Bicerano, Prediction of Polymer Properties, 2nd edition, Marcel Dekker, Inc, NY, 1996. 

29. R.N. Walters and R.E. Lyon, “Molar Group Contributions to Polymer Flammability,” 

Journal of Applied Polymer Science, 87, 548-563, 2003. 

57/58
APPENDIX A—TABULAR DATA FOR POLYMERS 

TABLE A-1. ONSET DECOMPOSITION (Td), PEAK MASS LOSS RATE (Tp), AND 

IGNITION (Tign) TEMPERATURES OF POLYMERS (AVERAGE VALUES ±10°C) 

POLYMER 

ISO/ASTM 

Abbreviation Td Tp Tign

Thermoplastics °C °C °C 

Acrylonitrile-butadiene-styrene ABS 390 461 394 

ABS FR ABS-FR − − 420 

Polybutadiene BDR 388 401 378 

Polyisobutylene (butyl rubber) BR 340 395 330 

Cellulose Acetate CA 250 310 348 

Cyanate Ester (typical) CE 448 468 468 

Polyethylene (chlorinated) CPE 448 476 −

Polyvinylchloride (chlorinated) CPVC − − 643 

Polychloroprene rubber CR 345 375 406 

Polychlorotrifluoroethylene CTFE 364 405 580 

Poly(ethylene-chlorotrifluorethylene) ECTFE 445 465 613 

Phenoxy-A EP − 350 444 

Epoxy (EP) EP 427 462 427 

Poly(ethylene-tetrafluoroethylene) ETFE 490 520 540 

Polyethylenevinylacetate EVA 448 473 

Fluorinated ethylene propylene FEP − − 630 

Poly(styrene-butadiene) HIPS 327 430 413 

Poly(styrene-butadiene) FR HIPS-FR − − 380 

Poly(p-phenyleneterephthalamide) KEVLAR 474 527 −

Polyarylate (liquid crystalline) LCP 514 529 −

Melamine formaldehyde MF 350 375 350 

Polyisoprene (natural rubber) NR 301 352 297 

Polytrifluoroethylene P3FE 400 405 −

Polyamide 12 PA12 448 473 −

Polyamide 6 PA6 424 454 432 

Polyamide 610 PA610 440 460 −

Polyamide 612 PA612 444 468 −

Polyamide 66 PA66 411 448 456 

Polyamide 6 (glass reinforced) PA6-G 434 472 390 

Polyamideimide PAI 485 605 526 

Polyacrylamide PAM 369 390 −

Polyacrylonitrile PAN 293 296 460 

Polyarylate (amorphous) PAR 469 487 −

A-1
TABLE A-1. ONSET DECOMPOSITION (Td), PEAK MASS LOSS RATE (Tp), AND 

IGNITION (Tign) TEMPERATURES OF POLYMERS (AVERAGE 

VALUES ±10°C) (Continued) 

POLYMER 

ISO/ASTM 

Abbreviation Td Tp Tign

Thermoplastics °C °C °C 

Polybutene PB − 390 −

Polybenzimidazole PBI 584 618 −

Polybutylmethacrylate PBMA 261 292 −

Polybenzobisoxazole PBO 742 789 −

Polybutyleneterephthlate PBT 382 407 382 

Polybutyleneterephthalate PBT-G 386 415 360 

Polycarbonate PC 476 550 500 

Polycarbonate/ABS (70/30) PC/ABS 421 475 440 

Polycarbonate (glass reinforced) PC-G 478 502 420 

Polycaprolactone PCL 392 411 −

Polyethylene (high density) PE HD 411 469 380 

Polyethylene (low density) PE LD 399 453 377 

Polyethylacrylate PEA 373 404 −

Polyethylene-acrylic acid salt PEAA 452 474 −

Polyetheretherketone PEEK 570 600 570 

Polyetherimide PEI 527 555 528 

Polyetherketone (e.g., KADEL) PEK 528 590 −

Polyetherketoneketone PEKK 569 596 −

Polyethylmethacrylate PEMA 246 362 −

Polyethylenenaphthalate PEN 455 495 479 

Polyethyleneoxide PEO 373 386 −

Polyethersulfone PESU 533 572 502 

Polyethyleneterephthlate PET 392 426 407 

Phenol formaldehyde PF 256 329 429 

Polytetrafluoroethylene-perfluoroether PFA − 578 −

Phenol formaldehyde PF-G − − 580 

Polymethylmethacrylate PMMA 354 383 317 

Poly(4-methyl-1-pentene) PMP − 377 −

Poly(α-methyl)styrene PMS 298 333 −

Poly(α-methylstyrene) PMS 250 314 −

Polyoxymethylene POM 323 361 344 

Polypropylene PP 354 424 367 

Polypropylene (isotactic) PP (iso) 434 458 −

A-2
TABLE A-1. ONSET DECOMPOSITION (Td), PEAK MASS LOSS RATE (Tp), AND 

IGNITION (Tign) TEMPERATURES OF POLYMERS (AVERAGE 

VALUES ±10°C) (Continued) 

POLYMER 

ISO/ASTM 

Abbreviation Td Tp Tign

Thermoplastics °C °C °C 

Polyphthalamide (AMODEL) PPA 447 488 −

Polyphenyleneether PPE − 418 426 

Poly(2,6-dimethylphenyleneoxide) PPO 441 450 418 

Polypropyleneoxide PPOX 292 343 −

Polyphenylenesulfide PPS 504 545 575 

Polyphenylsulfone PPSU 557 590 575 

Polystyrene PS 319 421 356 

Polysulfone PSU 481 545 510 

Polytetrafluoroethylene PTFE 545 590 630 

Polytetramethyleneoxide PTMO − 352 −

PU (isocyanurate/rigid) PU 271 422 378 

Polyetherurethane rubber PUR 324 417 356 

Polyvinylacetate PVAC 319 340 −

Polyvinylbutyral* PVB 333 373 −

Polyvinylchloride (50% DOP) PVC (flex) 249 307 318 

Polyvinylchloride (rigid) PVC (rigid) 273 285 395 

Polyvinylchloride/polyvinylacetate blend PVC/PVAC 255 275 −

Polyvinylidenechloride PVDC 225 280 −

Polyvinylidenefluoride PVDF 440 490 643 

Polyvinylfluoride PVF 361 435 476 

Polyvinylcarbazole PVK 356 426 −

Polyvinylalcohol PVOH 298 322 −

Polyvinylpyridine PVP 385 408 −

Polypara(benzoyl)phenylene PX 476 602 −

Poly(styrene-acrylonitrile) SAN 389 412 368 

Phenylsilsesquioxane (silicone) Resin SI 475 541 −

Silicone Rubber SIR 456 644 407 

Poly(tyrene-maleic anhydride) SMA 337 388 −

Polyimide thermoplastic TPI 523 585 600 

Polyurethane thermoplastic TPU 314 337 271 

Unsaturated Polyester UPT 330 375 380 

Unsaturated Polyester UPT-G − − 395 

A-3
TABLE A-2. LATENT HEAT OF GASIFICATION, CHAR YIELD, AND ENTHALPY OF 

GASIFICATION OF POLYMERS 

Lg μ hg

Polymer kJ/g g/g kJ/g 

ABS 2.3 0.00 2.3 

ABS-FR 2.5 0.00 2.5 

CEA 4.0 0.36 2.6 

CEE 4.1 0.42 2.4 

CEF 3.0 0.55 1.3 

CEM 3.0 0.26 2.2 

CEN 3.0 0.52 1.4 

CET 3.5 0.35 2.3 

CPE (25% Cl) 2.1 0.00 2.1 

CPE (36% Cl) 2.8 0.20 2.2 

CPVC 2.0 0.00 2.0 

CR 2.0 0.13 1.7 

ECTFE 1.5 0.00 1.5 

EP 1.6 0.04 1.5 

EPDM 1.9 0.00 1.9 

EP (30% fiberglass) 2.3 0.30 1.6 

ETFE 1.1 0.00 1.1 

FEP 1.5 0.00 1.5 

HIPS 2.0 0.00 2.0 

HIPS-FR 2.1 0.10 1.9 

PA6 1.5 0.02 1.5 

PA66 2.1 0.04 2.0 

PAI 4.8 0.61 1.9 

PBI 5.5 0.75 1.4 

PBT 1.4 0.07 1.3 

PBT-FR 2.3 0.15 2.0 

PC 2.4 0.25 1.8 

PC-FR 3.5 0.52 1.7 

PE HD 2.2 0.00 2.2 

PE LD 1.9 0.00 1.9 

PEEK 3.4 0.54 1.6 

PEI 3.5 0.53 1.7 

PEN 2.5 0.18 2.0 

PESU 3.8 0.40 2.3 

PET 1.4 0.05 1.3 

PF 5.4 0.60 2.2 

A-4
TABLE A-2. LATENT HEAT OF GASIFICATION, CHAR YIELD, AND ENTHALPY OF 

GASIFICATION OF POLYMERS (Continued) 

Lg μ hg

Polymer kJ/g g/g kJ/g 

PMMA 1.7 0.00 1.7 

POM 2.4 0.00 2.4 

PP 1.9 0.00 1.9 

PPS 3.8 0.50 1.9 

PPSU 4.3 0.58 1.8 

PS 1.8 0.00 1.8 

PSU 2.0 0.28 1.4 

PTFE 2.5 0.00 2.5 

PU 2.3 0.13 2.0 

PVC (flexible) 1.3 0.08 1.2 

PVC (rigid) 2.3 0.09 2.1 

PVDF 4.0 0.23 3.1 

PVF 1.9 0.00 1.9 

PX 6.4 0.66 2.2 

SIR 2.3 0.00 2.3 

TPU 2.4 0.13 2.1 

TABLE A-3. POLYMER THERMAL CONDUCTIVITY, DENSITY, HEAT CAPACITY, 

AND THERMAL DIFFUSIVITY AT ROOM TEMPERATURE 

Polymer 

κ 

(W/m-K)

ρ 

(kg/m3)

cp

(kJ/kg-K)

α 

(m2/s x 107)

ABS 0.26 1050 1.50 1.65 

BDR 0.22 970 1.96 1.16 

BR 0.13 920 1.96 0.72 

CA 0.25 1250 1.67 1.20 

CAB 0.25 1200 1.46 1.43 

CAP 0.25 1205 1.46 1.42 

CE 0.19 1230 1.11 1.39 

CN 0.23 1375 1.46 1.15 

CP 0.20 1300 1.46 1.05 

CPVC 0.48 1540 0.78 4.00 

CR 0.19 1418 1.12 1.20 

CTFE 0.23 1670 0.92 1.50 

DAP 0.21 1350 1.32 1.18 

DAP-G 0.42 1800 1.69 1.38 

A-5
TABLE A-3. POLYMER THERMAL CONDUCTIVITY, DENSITY, HEAT CAPACITY, 

AND THERMAL DIFFUSIVITY AT ROOM TEMPERATURE (Continued) 

Polymer 

κ 

(W/m-K)

ρ 

(kg/m3)

cp

(kJ/kg-K)

α 

(m2

/s x 107)

EAA 0.26 945 1.62 1.70 

ECTFE 0.16 1690 1.17 0.81 

EP 0.19 1200 1.7 1.12 

EPDM 0.20 930 2.0 1.08 

EP-G 0.42 1800 1.60 1.46 

EPN 0.19 1210 1.26 1.25 

ETFE 0.24 1700 1.0 0.66 

EVA 0.34 930 1.37 2.67 

FEP 0.25 2150 1.17 0.99 

HIPS 0.22 1045 1.4 1.54 

LCP 0.20 1350 1.20 1.24 

MF 0.25 1250 1.67 1.20 

MF-G 0.44 1750 1.67 1.51 

NBR 0.25 1345 1.33 1.40 

NR 0.14 920 1.55 0.98 

P3FE 0.31 1830 1.08 1.41 

PA11 0.28 1120 1.74 1.44 

PA11-G 0.37 1350 1.76 1.56 

PA12 0.25 1010 1.69 1.46 

PA6 0.24 1130 1.55 1.37 

PA610 0.23 1100 1.51 1.38 

PA612 0.22 1080 1.59 1.28 

PA66 0.23 1140 1.57 1.29 

PA6-G 0.22 1380 1.34 1.19 

PAEK 0.30 1300 1.02 2.27 

PAI 0.24 1420 1.00 1.69 

PAN 0.26 1150 1.30 1.74 

PAR 0.18 1210 1.20 1.24 

PB 0.22 920 2.09 1.14 

PBI 0.41 1300 0.93 3.40 

PBT 0.22 1350 1.61 1.01 

PC 0.20 1200 1.22 1.36 

PC-G 0.21 1430 1.10 1.34 

PE (HD) 0.43 959 2.00 2.24 

PE (LD) 0.38 925 1.55 2.65 

PE (MD) 0.40 929 1.70 2.53 

A-6
TABLE A-3. POLYMER THERMAL CONDUCTIVITY, DENSITY, HEAT CAPACITY, 

AND THERMAL DIFFUSIVITY AT ROOM TEMPERATURE (Continued) 

Polymer 

κ 

(W/m-K)

ρ 

(kg/m3)

cp

(kJ/kg-K)

α 

(m2

/s x 107)

PEEK 0.20 1310 1.70 0.90 

PEI 0.23 1270 1.22 1.48 

PEKK 0.22 1280 1.00 1.72 

PEMA 0.18 1130 1.47 1.08 

PEO 0.21 1130 2.01 0.90 

PESU 0.18 1400 1.12 1.15 

PET 0.20 1345 1.15 1.29 

PET-G 0.29 1700 1.20 1.42 

PF 0.25 1300 1.42 1.35 

PFA 0.25 2150 1.0 1.16 

PF-G 0.40 1850 1.26 1.72 

PI 0.11 1395 1.10 0.72 

PI-TS 0.21 1400 1.13 1.33 

PMMA 0.20 1175 1.40 1.19 

PMP 0.17 834 1.73 1.18 

PMS 0.20 1020 1.28 1.53 

POM 0.23 1420 1.37 1.18 

PP 0.15 880 1.88 0.89 

PPA 0.15 1170 1.40 0.92 

PPE 0.23 1100 1.19 1.76 

PPO 0.16 1100 1.25 1.16 

PPO-G 0.17 1320 1.31 0.98 

PPS 0.29 1300 1.02 2.19 

PPSU 0.18 1320 1.01 1.35 

PS 0.14 1045 1.25 1.04 

PS-G 0.13 1290 1.05 0.96 

PSU 0.26 1240 1.11 1.89 

PTFE 0.25 2150 1.05 1.11 

PU 0.21 1265 1.67 0.99 

PUR 0.19 1100 1.76 0.98 

PVAC 0.16 1190 1.33 1.03 

PVC (flex) 0.17 1255 1.38 0.98 

PVC (rigid) 0.19 1415 0.98 1.34 

PVDC 0.13 1700 1.07 0.91 

PVDF 0.13 1760 1.12 0.68 

PVF 0.13 1475 1.30 0.72 

A-7
TABLE A-3. POLYMER THERMAL CONDUCTIVITY, DENSITY, HEAT CAPACITY, 

AND THERMAL DIFFUSIVITY AT ROOM TEMPERATURE (Continued) 

Polymer 

κ 

(W/m-K)

ρ 

(kg/m3)

cp

(kJ/kg-K)

α 

(m2

/s x 107)

PVK 0.16 1265 1.23 1.02 

PVOH 0.20 1350 1.55 0.96 

PX 0.32 1220 1.3 2.02 

SAN 0.15 1070 1.38 1.02 

SBR 0.17 1100 1.88 0.82 

SI-G 0.30 1900 1.17 1.35 

SIR 0.23 970 1.59 1.49 

UF 0.25 1250 1.55 1.29 

UPT 0.17 1230 1.30 1.06 

UPT-G 0.42 1650 1.05 1.85 

VE 0.25 1105 1.30 1.74 

TABLE A-4. SURFACE ABSORPTIVITY OF POLYMERS 

Radiant Energy Source 

Polymer 

1000 K 

Blackbody 

1500 K 

Blackbody Flames Solar 

BR 0.92 0.93 0.92 0.95 

CR 0.72 0.63 0.71 0.62 

HIPS 0.86 0.75 0.88 0.29 

NR 0.88 0.82 0.89 0.69 

PA66 0.93 0.90 0.93 0.63 

PC 0.87 0.83 0.88 0.69 

PE LD 0.92 0.88 0.93 0.57 

PMMA (black) 0.94 0.94 0.94 0.96 

PMMA (clear) 0.85 0.69 0.89 0.097 

PP 0.87 0.83 0.86 0.62 

PPO 0.86 0.78 0.88 0.48 

PS (clear) 0.75 0.60 0.78 0.095 

PVC (flex) 0.90 0.90 0.91 0.89 

SIR 0.79 0.66 0.79 0.62 

A-8
TABLE A-5. EFFECTIVE HEAT OF COMBUSTION, HEAT OF COMPLETE 

COMBUSTION OF FUEL GASES (hc

0

), AND FLAMING COMBUSTION EFFICIENCY (χ) 

Polymer 

HOC 

(kJ/g) 

hc

0

(kJ/g) χ

CEN 20.6 20.7 1.00 

CEE 25.1 25.3 0.99 

PMMA 24.8 25.0 0.99 

PP 41.9 43.0 0.97 

PE LD 40.3 41.4 0.97 

PUR 24.0 24.7 0.97 

PE HD 40.3 41.6 0.97 

CET 25.9 26.9 0.96 

PAI 15.3 15.9 0.96 

CR 17.6 18.5 0.95 

CEM 28.9 30.6 0.94 

PEI 21.8 23.2 0.94 

CEA 25.9 27.6 0.94 

UPT 23.4 25.0 0.94 

POM 14.4 15.4 0.94 

TPU 23.5 25.4 0.93 

PPA 24.2 26.2 0.92 

CEF 16.9 18.3 0.92 

PA66 25.2 27.4 0.92 

PEEK 21.3 23.2 0.92 

PBT 21.7 23.8 0.91 

PSU 20.4 22.4 0.91 

PC 21.2 23.3 0.91 

PEN 22.9 25.2 0.91 

PPZ 15.0 16.6 0.90 

PESU 22.4 24.9 0.90 

PA6 25.8 28.7 0.90 

PPSU 23.5 27.0 0.87 

PPS 25.4 29.3 0.87 

PBI 22.0 26.5 0.83 

SBR 31.5 38.0 0.83 

EVA 30.8 37.9 0.81 

NR 30.2 37.9 0.80 

SIR 21.7 27.2 0.80 

PPO/PS 21.3 26.9 0.79 

ABS 29.0 36.6 0.79 

A-9
TABLE A-5. EFFECTIVE HEAT OF COMBUSTION, HEAT OF COMPLETE 

COMBUSTION OF FUEL GASES (hc

0

), AND FLAMING 

COMBUSTION EFFICIENCY (χ) (Continued) 

Polymer 

HOC 

(kJ/g) 

hc

0

(kJ/g) χ

EPDM 29.2 37.9 0.77 

CTFE 6.5 8.5 0.76 

HIPS 28.1 37.2 0.76 

EP 20.4 27.1 0.75 

PET 18.0 24.1 0.75 

LCP 14.8 20.6 0.72 

CPE (25% Cl) 22.6 31.6 0.72 

VE 22.0 31.1 0.71 

ETFE 7.3 10.8 0.68 

PS 27.9 42.0 0.66 

PU 16.3 25.4 0.64 

PX 20.0 31.3 0.64 

PVC (flexible) 11.3 19.3 0.59 

PTFE 4.6 8.4 0.55 

PVC (rigid) 9.3 18.6 0.50 

PS-FR 13.8 33.0 0.42 

CPE (36% Cl) 10.6 26.3 0.40 

TPI 12.0 31.6 0.38 

ABS-FR 10.2 26.9 0.38 

PVDF 3.8 10.4 0.36 

CPE (48% Cl) 7.2 20.2 0.36 

ECTFE 4.6 13.6 0.34 

CPVC 3.9 12.8 0.30 

PVF 4.1 18.5 0.22 

FEP 1.3 7.7 0.17 

A-10
TABLE A-6. LIMITING HEAT RELEASE RATE (HRR0), HEAT RELEASE PARAMETER, 

LIMITING OXYGEN INDEX, UL 94 RATING, AND HEAT RELEASE CAPACITY (ηc) 

Polymer 

HRR0 

(kW/m2) 

HRP 

(kJ/kJ) 

LOI, [O2] 

(% v/v) 

UL 94 

Rating 

ηc

(J/g-K)

HIPS 510 ±77 14 ±2 18 HB 893 

PP 369 ±79 22 ±2 17 HB 1200 

PET 424 ±168 13 ±4 20 HB 402 

PS 410 ±66 17 ±2 18 HB 1040 

ABS 359 ±66 13 ±2 18 HB 669 

PBT 341 ±106 15 ±3 23 HB 474 

PE (chlorinated) − − 21 HB 693 

UPT 261 ±105 11 ±2 20 HB −

PC/ABS 259 ±43 11 ±1 − HB −

PA66 240 ±59 18 ±2 24 HB 600 

PMMA 217 ±47 13 ±1 17 HB 574 

PS-FR 205 ±27 7 ±1 − V2 −

PPO/PS 192 ±22 15 ±1 − HB −

PA6 187 ±55 18 ±2 24 HB 487 

PC/ABS-FR 178 ±36 7 ±1 − V1 −

VET 169 ±44 13 ±1 − HB 805 

PESU 168 ±23 4 ±0 36 V1 345 

HIPS-FR 164 ±30 5 ±1 − V2 −

POM 162 ±30 6 ±1 15 HB 398 

EP 160 ±46 10 ±1 19 HB 657 

PE 145 ±93 21 ±3 17 HB 1560 

PBT-FR 141 ±130 6 ±3 − V2 −

CEA 112 ±22 7 ±2 24 V1 273 

ABS-FR 117 ±33 6 ±1 − V2 301 

HIPS-FR 114 ±36 4 ±1 − V0 −

PVC (flex) 91 ±19 4 ±0 − V2 −

SIR (filled) 90 ±13 5 ±0 32 V0 88 

PC 89 ±32 9 ±1 25 V2 390 

PEN 57 ±13 5 ±0 32 V2 309 

ETFE 44 ±31 6 ±0 30 V0 198 

PVC (rigid) 9 ±25 3 ±1 45 V0 138 

CR − 9 40 V0 188 

KEVLAR − 32 V0 302 

HB = Horizontal burning 

V = vertical 

A-11
TABLE A-6. LIMITING HEAT RELEASE RATE (HRR0), HEAT RELEASE PARAMETER, 

LIMITING OXYGEN INDEX, UL 94 RATING, AND HEAT RELEASE 

CAPACITY (ηc) (Continued) 

Polymer 

HRR0 

(kW/m2) 

HRP 

(kJ/kJ) 

LOI, [O2] 

(% v/v) 

UL 94 

Rating 

ηc

(J/g-K)

UPT-FR -31 ±10 2 ±0 − V0 −

CPVC -34 ±9 3 ±0 52 V0 −

PE (crosslinked)-FR -38 ±28 5 ±5 − V0 −

PAI -64 ±16 2 ±0 45 V0 33 

PPSU -83 ±25 4 ±0 38 V0 115 

PTFE -84 ±9 2 ±0 95 V0 35 

PEEK -94 ±20 3 ±0 35 V0 155 

NOMEX − − 28 V0 152 

PEI -113 ±19 3 ±0 47 V0 121 

ECTFE -127 ±6 4 ±0 60 V0 −

PPS -147 ±30 6 ±1 44 V0 164 

PBI -150 ±36 3 ±0 36 V0 41 

PC-FR -191 ±51 4 ±1 56 V0 30 

FEP − 2 95 V0 57 

HB = Horizontal burning 

V = vertical 

TABLE A-7. SMOKE EXTINCTION AREA OF POLYMERS 

Polymer 

Smoke 

Extinction 

Area 

(m2/kg) 

PTFE 33 

CPVC 33 

POM 50 

Douglas Fir (wood) 75 

PI 75 

PMMA 100 

PBI 100 

PAI 120 

PA6 134 

Hemlock (wood) 150 

PEI 150 

PES 150 

A-12
TABLE A-7. SMOKE EXTINCTION AREA OF POLYMERS (Continued) 

Polymer 

Smoke 

Extinction 

Area 

(m2/kg) 

PA66 230 

PEEK 292 

PAS 300 

PE 325 

PF 325 

PET 400 

PP 455 

PSU 475 

PU 550 

PBT 623 

PPS 646 

PVC flex/FR 770 

PEKK 800 

UPT 800 

PC 891 

PMMA/PVC alloy 900 

EP 907 

ABS 925 

BMI 950 

PVC rigid 1015 

VE 1050 

PVC flex 1078 

PS 1150 

PPO 1300 

ABS (Br FR) 1500 

Silicone Elastomers 1500 

EP (Br FR) 1600 

PS (Br FR) 1650 

A-13/A-14