ISO/TR 13387-4:1999

Fire safety engineering — Part 4: Initiation and development of fire and generation of fire effluents

Ingénierie de la sécurité contre l'incendie — Partie 4: Amorçage et développement des feux et production des effluents du feu

Požarno inženirstvo - 4. del: Začetek in razvoj požara in dimnih plinov

General Information

• Status: Withdrawn
• Publication Date: 29-Sep-1999
• Withdrawal Date: 29-Sep-1999
• ICS: 13.220.01 - Protection against fire in general
• Technical Committee: ISO/TC 92/SC 4 - Fire safety engineering
• Drafting Committee: ISO/TC 92/SC 4 - Fire safety engineering
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 22-Apr-2014
• Completion Date: 14-Feb-2026
• Ref Project: SIST ISO/TR 13387-4:2001 - Fire safety engineering -- Part 4: Initiation and development of fire and generation of fire effluents

Standards Content (Sample)

TECHNICAL ISO/TR
REPORT 13387-4
First edition
1999-10-15
Fire safety engineering —
Part 4:
Initiation and development of fire and
generation of fire effluents
Ingénierie de la sécurité contre l'incendie —
Partie 4: Amorçage et développement des feux et production des effluents
du feu
A
Reference number
Contents
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Symbols and abbreviated terms .3
5 Subsystem 1 of the total design system .5
6 Subsystem 1 evaluations.5
6.1 General.5
6.2 Initiation of fire.6
6.3 Fire development .13
6.4 Smoke production .20
6.5 Species generation.23
7 Engineering methods .27
7.1 General.27
7.2 Estimation formulae .28
7.3 Computer models .28
7.4 Experimental methods .29
(informative)
Annex A Smoke measurement units .31
Bibliography.33
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet [e-mail]
Printed in Switzerland
ii
© ISO
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The main task of ISO technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
 type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
 type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
 type 3, when a technical committee has collected data of a different kind from that which is normally published
as an International Standard (“state of the art“, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until the data they provide are considered to be no longer valid or useful.
ISO/TR 13387-4, which is a Technical Report of type 2, was prepared by Technical Committee ISO/TC 92, Fire
safety, Subcommittee SC 4, Fire safety engineering.
It is one of eight parts which outlines important aspects which need to be considered in making a fundamental
approach to the provision of fire safety in buildings. The approach ignores any constraints which might apply as a
consequence of regulations or codes; following the approach will not, therefore, necessarily mean compliance with
national regulations.
ISO/TR 13387 consists of the following parts, under the general title Fire safety engineering:
 Part 1: Application of fire performance concepts to design objectives
 Part 2: Design fire scenarios and design fires
 Part 3: Assessment and verification of mathematical fire models
 Part 4: Initiation and development of fire and generation of fire effluents
 Part 5: Movement of fire effluents
 Part 6: Structural response and fire spread beyond the enclosure of origin
 Part 7: Detection, activation and suppression
 Part 8: Life safety — Occupant behaviour, location and condition
Annex A of this part of ISO/TR 13387 is for information only.
iii
© ISO
Introduction
Evaluation of the initiation and development of fire and the generation of smoke and toxic species is an essential
step in the fire safety design of buildings, processes, etc. These phenomena have been actively studied especially
during the last twenty years. Calculation methods and computer codes have been developed to make the
necessary evaluations. At the same time, advances in experimental techniques have made it possible to produce
input data for the calculation methods and to run large-scale tests for assessing the validity and limitations of the
models.
In most of the existing fire safety regulations, measures are taken to prevent the ignition of a fire by controlling the
use of materials and by controlling the amount and location of possible ignition sources. It is not, however, possible
to prevent all ignitions, and therefore measures are taken to control the fire development and the generation of
smoke and toxic species. In most of the existing building regulations, ignitability, flame spread, burning rate, smoke
production and toxic-species production are controlled by what are known as reaction-to-fire and flammability
classifications. These are to a great extent empirical and based on product performance in a specific small-scale
test. Similar regulations have been set on building contents, e.g. upholstered furniture, stored goods, etc., in some
countries.
A more modern approach for prescriptive regulations is to establish the classification scheme based on small-scale
tests in such a fashion that relative performance in one or more full-scale fire scenarios is replicated. If the
scenarios are sufficiently representative of real fire scenarios, the classification system becomes more reliable than
those based on performance in small-scale tests alone.
In this document, the initiation and development of fire and the generation of hazardous species is considered as
part of a global fire safety evaluation system. This part of ISO/TR 13387 is intended for use together with the other
parts as described in clause 6. For some applications, this part alone may be sufficient.
Clause 6 of this part of ISO/TR 13387 describes and provides guidance on the methods available to describe the
physical and chemical processes involved in:
 initiation of fire;
 fire development;
 smoke generation;
 toxic-species generation.
Clause 7 is a discussion of the engineering methods available to evaluate the initiation and development of fire and
the generation of smoke and gaseous species.
Quantitative information may be related to specific test conditions and/or specific commercial products, and thus the
application of data under different conditions may result in significant errors.
iv
TECHNICAL REPORT  © ISO ISO/TR 13387-4:1999(E)
Fire safety engineering —
Part 4:
Initiation and development of fire and generation of fire effluents
1 Scope
This part of ISO/TR 13387 is intended to provide guidance to designers, regulators and fire safety professionals on
the use of engineering methods for the prediction of the initiation of fire, the generation of fire effluents and the
development of fire inside the room of origin. It is not intended as a detailed design guide, but could be used as the
basis for the development of such a guide.
This part of ISO/TR 13387 provides a framework for critically reviewing the suitability of an engineering method for
assessing the potential for the initiation and development of fire and the generation of fire effluents. It also provides
guidance on the means to assess the effectiveness of fire safety measures meant to reduce the probability of
ignition, to control fire development and to reduce the accumulation of heat, smoke and toxic products or products
causing non-thermal damage. The methods for calculating the effects of design fires for use in the design and
assessment of fire safety of a building are also addressed.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO/TR 13387. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this part of ISO/TR 13387 are encouraged to
investigate the possibility of applying the most recent additions of the normative documents indicated below. For
undated references, the latest addition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid international standards.
ISO 31-0:1992, Quantities and units — Part 0: General principles.
ISO 1000:1992, SI units and recommendations for the use of their multiples and certain other units.
ISO 5660-1:1993, Fire tests — Reaction to fire — Part 1: Rate of heat release from building products — (Cone
calorimeter method).
ISO 7345:1987, Thermal insulation — Physical quantities and definitions.
ISO 9705:1993, Fire tests — Full-scale room test for surface products.
ISO/TR 11696-1, Use of reaction to fire tests — Part 1: Application of results to predict fire performance of building
products by mathematical modelling.
ISO/TR 13387-1, Fire safety engineering — Part 1: Application of fire performance concepts to design objectives.
ISO/TR 13387-2, Fire safety engineering — Part 2: Design fire scenarios and design fires.
© ISO
ISO/TR 13387-3, Fire safety engineering — Part 3: Assessment and verification of mathematical fire models.
ISO/TR 13387-5, Fire safety engineering — Part 5: Movement of fire effluents.
ISO/TR 13387-6, Fire safety engineering — Part 6: Structural response and fire spread beyond the enclosure of
origin.
ISO/TR 13387-7, Fire safety engineering — Part 7: Detection, activation and suppression.
ISO/TR 13387-8, Fire safety engineering — Part 8: Life safety — Occupant behaviour, location and condition.
ISO 13571, Fire hazard analysis — Life-threatening components of fire.
ISO 13943, Fire safety — Vocabulary.
3 Terms and definitions
For the purposes of this part of ISO/TR 13387, the terms and definitions given in ISO 13943 and ISO/TR 13387-1
and the following apply.
3.1
emissivity
the ratio of the power per unit area radiated from a surface to that radiated from a black body at the same
temperature
3.2
extinction coefficient
a constant determining the decay of the light intensity in smoke per unit path length, given by K = (1/l) ln (I /I)
–1
It is expressed in m .
3.3
fire exposure
a process by which, or the extent to which, humans, animals, materials, products or assemblies are subjected to the
conditions created by a fire
3.4
heat flux
the rate at which heat crosses a surface per unit area of surface, expressed in W/m
In ISO 1000 and ISO 31-0, this is referred to as "density of heat flow rate".
3.5
heat of combustion
the energy which unit mass of material or product is capable of releasing by complete combustion, expressed in
J/kg
3.6
heat of gasification
the quantity of energy required to change a unit mass of material from condensed phase to vapour without change
of temperature, expressed in J/kg
3.7
ignition temperature
the minimum temperature measured on a material at which sustained combustion can be initiated under specific
test conditions, expressed in K
3.8
opening factor
1/2
A (h ) /A
v v T
© ISO
1/2
It is expressed in m .
For the meanings of the symbols, see clause 4.
3.9
pyrolysis
a process of simultaneous phase and chemical-species change caused by heat
3.10
smoke point
minimum height of a laminar axisymmetric diffusion flame (fuel volumetric mass loss rate) at which smoke escapes
from the tip of a flame, expressed in m
3.11
specific heat capacity
heat capacity divided by mass, expressed in J/(kg×K)
3.12
thermal conductivity
r
ratio of heat flux to temperature gradient, defined by the relation -·qk= ∇ T
It is expressed in W/(m×K).
3.13
thermal diffusivity
k
thermal conductivity divided by the density and the specific heat capacity, given by k = k/rc
It is expressed in m /s.
3.14
thermal inertia
the product of the thermal conductivity, the density and the specific heat capacity, given by
krc
2 4 2
It is equal to the square of thermal effusivity as defined in ISO 7345. It is expressed in J /(m ×K ×s).
3.15
total cross-sectional area of smoke
the average cross-sectional area of smoke particles perpendicular to the light path multiplied by the number of
smoke particles, expressed in m
3.16
ventilation factor
1/2
A (h )
v v
5/2
It is expressed in m .
For the meanings of the symbols, see clause 4.
4 Symbols and abbreviated terms
A area of an opening, expressed in m
v
A surface area of fuel, expressed in m
fuel
A floor area, expressed in m
F
A total area of the bounding surfaces in an enclosure, expressed in m
T
¢¢
© ISO
-2
–2
&at , expressed in W×s
Q
g
1/2
F opening factor, expressed in m
5/2
F ventilation factor, expressed in m
V
f yield of species X, where X = CO, CO , etc.
X 2
g acceleration due to gravity, expressed in m/s
h height of an opening, expressed in m
v
I intensity of light after passing through smoke, expressed in W/m
I intensity of light in clean air, expressed in W/m
k thermal conductivity, expressed in W/(m×K)
–1
K extinction coefficient, expressed in m
kthermal diffusivity, expressed in W/(m×K)
l optical path length, expressed in m
L thickness of a specimen, expressed in m
m smoke density, expressed in dB/m
mass loss rate of fuel, expressed in kg/s
m&
fuel
generation rate of species X, where X = CO, CO , etc., expressed in kg/s
m&
X
N total number of smoke particles
–3
n number density of smoke particles, expressed in m
ffuel to air equivalence ratio
&
Q heat release rate, expressed in W
&
heat release rate at the growth time in t fires, expressed in W; usually taken as 1 MW
Q
r
q heat flux (density of heat flow rate), expressed in W/m
q& external heat flux, expressed in W/m
ext
q& heat loss from the surface by convection or radiation, expressed in W/m
loss
rdensity, expressed in kg/m
seffective absorption cross-section of a smoke particle, expressed in m
T temperature, expressed in °C
T ignition temperature, expressed in °C
ig
T the lowest temperature at which a flammable mixture at its lean limit may burn, expressed in °C
L
T initial surface temperature, expressed in °C
¢¢
¢¢
¢¢
© ISO
T the lowest temperature at which a flammable mixture at its rich limit may burn, expressed in °C
U
t time, expressed in s
t growth time in a t fire, expressed in s
g
t time to ignition (ignition delay), expressed in s
ig
ttime constant, expressed in s
& volume flow rate, expressed in m /s
V
f
V volumetric production rate of species X, where X = CO, CO , etc., expressed in m /s
X 2
x flame height, expressed in m
f
x position of pyrolysis front, expressed in m
p
5 Subsystem 1 of the total design system
The approach adopted in the work of ISO/TC 92/SC 4 is to consider the global objective of fire safety design. The
global design, described in more detail in ISO/TR 13387-1, is sub-divided into what are called "subsystems" of the
total design. A key principle is that inter-relation and interdependence of the various subsystems are appreciated,
and that the consequences of all the events in any one subsystem on all other subsystems are identified and
addressed. Another key principle is that the design is time-based to reflect the fact that real fires vary in severity and
extent with time. Ignition represents zero time.
In ISO/TR 13387-1, the total fire safety design is illustrated by an information bus analogy. The information bus has
three layers: global information, evaluation information and process information. In this information bus analogy,
subsystem 1 (SS1) concerns the initiation and development of fire and generation of fire effluent and is illustrated in
Figure 1. SS1 draws on other subsystems for the prescription or characterization of a fire and, in turn, provides
information for the other subsystems to employ. Definitions of terms concerning the global information bus are given
in ISO/TR 13387-1.
For example, SS1 provides the information on heat, smoke and species generation, which is then used by SS2 for
the calculation of smoke movement out of the room and in the building and by SS5 to assess evacuation and
rescue provisions. SS1 also calculates the temperature history in the enclosure of fire origin, which then is
employed by SS3 to predict the structural behaviour. The temperature and flow profiles in the room are employed
by SS4 to predict the detection of fire, as well as the activation of smoke control and suppression systems. The time
of activation of active control systems is then fed back by SS4 to SS1 for the prediction of subsequent fire
development and smoke and species generation. The initiation of a fire and its development outside the enclosure
of origin are also calculated by SS1.
The evaluations, and processes needed to do the evaluations, are discussed in detail in clause 6.
6 Subsystem 1 evaluations
6.1 General
In this clause, various fire phenomena and consequences of fire will be discussed. The required input information
and the possible output information will be identified. Areas for which shortages in engineering methods and lack of
knowledge are known to exist will be addressed. The text makes reference to existing acknowledged literature,
whenever such is available.
© ISO
6.2 Initiation of fire
6.2.1 Evaluation of initiation of fire
In deterministic fire safety engineering design, ignition is often simply assumed to occur and no calculations on the
ignition process are performed. In other instances, especially when the combustible contents and the distribution of
ignition sources in the room of fire origin are known, performing calculations on the ignition process can provide
valuable information on the possible fire development in the room. Evaluation of ignition is needed especially when
the fire safety engineer has to evaluate whether one product can be replaced by another, all other design
parameters being fixed. Often the task is to consider if a potential ignition source is likely to cause ignition of
adjacent items, i.e. if the first item ignited will cause a second item to be ignited, and thereby the fire to spread to a
hazardous extent.
© ISO
Figure 1 — Illustration of the global information, evaluation and process buses for SS1
© ISO
The probability of ignition is a subset of design fires which is addressed in ISO/TR 13387-2. Assessment of the
probability of ignition is needed when making decisions about the design fire scenarios and event trees used in risk
assessment. Probabilistic design and risk assessment are discussed in more detail in ISO/TR 13387-1.
This subclause discusses ignition of items which are in one way or another exposed to heating from an external
source. This source of heat can be of various intensities and shapes, varying from (say) a match flame to an
actively burning fuel package. Fire development as discussed in 6.3 can be considered to be a series of non-
simultaneous ignitions, each of which generally behaves in the theoretical manner discussed herein.
Figure 2 identifies parameters having an influence on the ignition of various kinds of fuel. A condition for ignition is
that both a flammable substance and an ignition source exist. The flammable substance may appear in a number of
different forms. The heat transfer from the ignition source to the flammable substance may also take different forms,
the processes being, in addition, sensitive to the local environment around the source and the exposed substance.
6.2.1.1 Input
The evaluation of the initiation of a fire (see Figure 1) requires as input information from the global information the
following:
 building parameters (e.g. lining materials, their thermal and chemical properties, their location with respect to
heat sources);
 fire loads (building contents, thermal and chemical properties of building contents, location with respect to heat
sources);
 fire scenarios (properties of ignition sources, their number and their locations);
 thermal profile (radiative, conductive and convective heat fluxes, gas temperature, initial fuel temperature);
 size of fire/extent of smoke (area exposed to a burning fire).
NOTE This information is also needed for evaluating the ignition of second, etc., items. Therefore, e.g. the size of
fire/extent of smoke is an input or output, depending on when it is used during an evaluation.
6.2.1.2 Output
The evaluation of the initiation of a fire (see Figure 1) provides the following information to the global information:
 fire scenarios (object first ignited, time to ignition);
 size of fire/ extent of smoke (area first ignited, size of initial flame).
6.2.2 Gas phase ignition
The process of ignition to give flames requires mixtures of gas phase combustibles at an appropriate fuel-to-air ratio
and either local temperature fields higher than the auto-ignition limit or a pilot source. The necessary conditions for
any gaseous mixture of fuel are usually expressed as ignitability regions as in Figure 3. If a fuel is not naturally in
the gas phase, energy must be applied to the substance to bring it to the gaseous state. For liquids, the amount of
energy required depends on the vaporisation rate and the way in which the liquid is distributed or the material upon
which the liquid is absorbed, i.e. bulk liquids will not ignite until the bulk temperature equals or exceeds the flash
point. If the liquid is atomised, its ignition propensity will approach the ignitability of gaseous mixtures of the same
material, depending on the degree of atomisation and the temperature of the environment. If the liquid is absorbed
in a porous medium, the energy demand for ignition will depend on how fast the porous material will absorb energy
and heat up. In this case, the thermal properties of the porous medium will dominate the process.
In the case of gaseous or liquid fuels, the engineering task is usually to consider whether a flammable mixture can
be created in the space of concern. In the case of solids, the task can usually be reduced to evaluating whether the
surface temperature will become high enough to cause ignition, and no gas phase considerations are needed as we
can see in 6.2.3.
© ISO
Figure 2 — Factors to be taken into account when assessing ignition potential
© ISO
Figure 3 — Effect of temperature on the limits of flammability of a flammable vapour/air mixture at constant
[1]
initial pressure
Useful information on gas phase ignition can be found in references [1] and [2].
6.2.2.1 Input
The evaluation of gas phase ignition may require, as input, specific information on the following processes and
product properties:
 fuel properties, e.g. latent heat of gasification, flash point, flammability limits, vaporisation or pyrolysis rate at
defined temperatures and thermal-exposure histories;
 radiative, convective and conductive heat transfer to the surfaces to estimate the fuel flow rate and the thermal
conditions in the space of interest;
 fuel/air mixing, e.g. the air flow in the space to estimate the dilution of the gaseous fuel;
 properties of potential ignition sources, e.g. temperature and spark energy.
Detailed discussions of the flammability of gas mixtures and ignition of liquid fuels, as well as tabulations of fuel
[3]
properties, can be found in various publications, e.g. the SFPE Handbook .
6.2.2.2 Output
The output of the evaluation is the time to ignition or whether ignition will occur at all.
© ISO
6.2.3 Ignition model for solids
Because most accidental fires in buildings are initiated on solid materials, this subclause is restricted to surveying
the parameters that dominate the ignition of materials in the solid phase.
Heat transferred from a source to a target results in a rise in the temperature of the target. The conditions for
ignition are produced when pyrolyzates from the target mix with air to produce ignitable mixtures at temperatures
that could locally exceed spontaneous-ignition temperatures. The presence of any kind of pilot source will generally
cause ignition as soon as the fuel/air ratio permits. Factors that control this process are the mode of ignition, the
rate of heat transfer from the source, the target composition, the target location, the thermal and optical properties
of the target and the availability of air. For common ignition sources (hot object, intense electric arc, smouldering
material or flame), two types of ignition are possible: (1) glowing ignition (exothermic reaction at the surface of a
material with air) and (2) flaming ignition (ignition that occurs in the gas phase mixture of pyrolyzates and air).
Materials that ignite to glowing ignition may smoulder (combustion that occurs and propagates in the bulk material)
for some period. If conditions are appropriate, smouldering may undergo a transition to flaming ignition and rapid fire
spread. Materials that are ignited to flaming ignition may sustain the flaming mode and, if conditions are right, may
spread to a larger size. Conversely, if the ignition experience is short, the flaming mode may be transient, and either
convert to glowing or smouldering, or simply self-extinguish. As with the ignition process, the transient or sustained
behaviour of the post-ignition condition is controlled by the composition and constitution of the material.
Regardless of ignition source, the response of a material to heating is dominated by the physical properties of the
material. A detailed discussion of the ignition of solids can be found in reference [4]. Useful information can also be
found in [5] and [6]. ISO/TC92/SC1 is working on a document describing the theoretical background of the ISO
reaction-to-fire tests (ISO/TR 11696-1). The document includes a discussion of ignition under radiant heat
exposure.
The thermal theory of ignition assumes that each material can be characterised by a critical ignition temperature
[7]
T . By using simple heat-conduction theory, one can show that, for thermally thick material behaviour, the ignition
ig
delay is given by:
2 2
&
t ∝ krc(T – T ) /( q – q& ) (1)
ig ig 0 ext loss
For thermally thin material behaviour, i.e. if the temperature in the material is approximately uniform, the ignition
delay is given by:
t ∝ rcL(T – T )/( q& – q& ) (2)
ig ig 0 ext loss
The loss term q& contains all the losses by re-radiation and convection.
loss
The product property term krc(T – T ) or rcL(T – T ) can be determined experimentally. This parameter has also
ig 0 ig 0
[8],[9]
been called a flux time product (FTP) , and the square root of the parameter a thermal-response parameter
[10]
(TRP) .
When deriving the equations above, all the properties have been taken as constants. In reality, the properties
depend on temperature and other ambient conditions. For example, under slow heating the surface may pyrolyze
sufficiently for the chemical properties to change, thus changing e.g. the ignition temperature. Usually, the
experimental data available is from tests with a pilot ignition source. Without a pilot flame, the critical ignition
temperature is considerably higher.
1/2
It may also be difficult to know whether the product is thermally thin or thick. The condition L >> (k t ) is widely
ig
used for characterising products with thermally thick behaviour. Another practical rule of thumb is that a product is
considered to show thermally thick behaviour if the physical thickness L is > 0,6rq& , where L is in mm, the density
ext
3 2 [8]
r in kg/m and the heat flux q& in kW/m .
ext
The loss term depends on the ambient conditions, specimen size and orientation, etc. For example, different
q&
loss
convective cooling of the surface may significantly influence the ignition delay time. One must therefore be very
careful when applying the numerical data obtained even in standardised tests like the ISO ignitability test or the
cone calorimeter. Proper corrections can be made if the conditions are sufficiently well defined.
¢¢
¢¢
¢¢
¢¢
¢¢ ¢¢
¢¢ ¢¢
© ISO
At ignition, the loss term ( q& ) is equal to the critical heat flux for ignition. This is derived by extrapolation from a
loss
limited number of tests at different levels of radiant heat flux. However, the true minimum heat flux for ignition may
be lower or higher because of the changes in the physical and chemical properties of the surface under extended
exposure. The significance of this discrepancy depends to a great extent on the application of the data.
Special attention has to be given if the product under consideration melts. Some polymers that have low melting
temperatures will melt away from moderate- to low-intensity ignition sources before the target attains its ignition
temperature. It is therefore possible that product information based on some standard tests may not guarantee low
flammability; under a higher exposure, the product may ignite easily.
The critical flux for ignition and the effective ignition temperature may be influenced by adding fire retardants to the
solid. For some fire retardants, the effect may be to decrease the time to ignition under specific conditions. The
benefit of the retardants is seen as a reduced burning rate.
In the above discussion, the intensity of the radiant source was assumed adequate to positively ignite a target.
Normally, pure radiant sources would not cause the primary ignition in an accidental fire sequence. However, fire
spread from an initially ignited item may occur by means of radiant heat transfer. Factors that define the radiant
intensity of a source fire are flame area and thickness. The flame volume determines the flame emissivity, which is
a number between 0 and 1. For hydrocarbon fuels, flames thicker than 1 m will generally have an emissivity
approaching 1. This factor dictates the efficiency with which radiant energy is transferred between source and
target. The flame size, along with the distance and angular intercepts between source and target, determines the
view factor, which is also a number between 0 and 1.
View factors for various ideal shapes of hot objects can be found in reference [11]. Very often, flames from pool fires
are treated as radiating cylinders the height of which depends on the burning rate or the heat release rate.
Flame size for most fuels is directly proportional to the mass burning rate or heat release rate. Correlation can then
[12]
be created to enable the calculation of the minimum safe distance from a burning item .
6.2.3.1 Input
The evaluation of the ignitability of solids may require, as input, specific information on the following processes and
product properties:
 fuel properties (thickness, surface emissivity, thermal conductivity, density, specific heat capacity, ignition
temperature under various conditions, critical radiant flux for piloted ignition);
 radiative, convective and conductive heat transfer to the surfaces to estimate the fuel flow rate and the thermal
conditions in the space of interest;
 properties of potential ignition sources, e.g. temperature and spark energy, size of flame.
6.2.3.2 Output
The output of the evaluation may be either the time to ignition or whether ignition is possible at all.
6.2.4 Ignition to smouldering
Materials which are prone to smouldering have particular chemical compositions, form char on decomposition and
are generally low density (e.g. flexible polyurethane foams, cotton batting and pulverized-paper insulation). Contact
with ignition sources such as cigarettes or hot surfaces can result in ignition which, if sustained, will propagate as
smouldering combustion.
For cellulosic materials, the initiation of smouldering requires that the cellulose be converted to char, and this can
[13]
occur after prolonged exposure to temperatures above 100 °C .
The same requirements have to be met for smouldering ignition of synthetic polymers to occur. In addition, these
materials require a prolonged, low-intensity ignition source. Note that many of the conditions that promote
smouldering combustion are similar to those necessary for self-ignition and spontaneous combustion, i.e. a material
that is susceptible to oxidation, and an environment where the heat generated by oxidation is contained by a
medium of low heat loss potential. Self-heating parameters are summarised succinctly in reference [14] and
¢¢
© ISO
exhaustively in [15]. Many other sources of useful information on the assessment of self-ignition potential are
available.
In the literature, the input data needed for evaluation of smouldering ignition is scarce. The self-ignition propensity is
usually evaluated by a series of small-scale tests from which parameters are derived to enable evaluation of the
critical storage temperature of a larger volume of the same product. The scaling laws are based on fundamental
theory, and the extrapolation to larger scale has turned out to be remarkably reliable in a great number of
applications.
6.3 Fire development
6.3.1 Evaluation of fire development
Evaluation of fire development is closely linked to the quantification of a design fire discussed in detail in
ISO/TR 13387-2. There are basically two distinctly different methods of determining the design fire for a given
scenario. One is based on knowledge of the amount, type and distribution of combustible materials in the
compartment of fire origin. The other is based on knowledge of the type of occupancy, where very little is known
about the details of the fire load.
The design fire and the fire development are usually quantified by the heat release rate (HRR) as a function of time.
Once the heat release rate is known, the flame height and the gas temperatures in the room can be estimated using
methods discussed later in this subclause. The external heating of a second object can then be calculated. The
development of the fire can then be considered to be a sequence of non-simultaneous ignitions, which generally
behave in the theoretical manner discussed in 7.1. A design fire can therefore be arrived at, using data from
experiments to estimate the heat release rate and using methods outlined in 7.1 for calculating the time to ignition.
In some cases, more detailed methods can be used to simulate fire development. These may be needed especially
when evaluating the relative fire safety of products in a specific application. Guidance on models of this kind will be
given in the following subclauses describing the processes of fire development. It should, however, be noted that for
design purposes the need for accurate data is not as high as for predicting the results of a single experiment. One
may never cover all the possible fire situations and, therefore, characteristic data based on statistical data for a
given occupancy must be applied.
Reference [16] provides a useful discussion about modelling fire growth from ignition to full involvement.
6.3.1.1 Input
The evaluation of the development of a fire (see Figure 1) requires as input information the following:
 building parameters (e.g. lining materials, thermal and chemical properties, location);
 fire loads (building contents, thermal and chemical properties of building contents, location);
 fire scenarios (e.g. experimentally determined characteristics of the first item ignited);
 thermal profile (radiative, conductive and convective heat fluxes, gas temperature, initial fuel temperature);
 building condition (conditions of the building products, e.g. due to pre-heating);
 contents condition (conditions of the building contents, e.g. due to pre-heating).
6.3.1.2 Output
The output data are:
 Size of fire/smoke (e.g. burning area, flame height, heat release rate, mass loss rate, smoke density in the
room);
 thermal profile (temperature and heat flux distribution in the room of origin);
© ISO
 pressure/velocity profile (e.g. pressure at smoke vents, flow through vents, velocity in the ceiling jet);
 building response;
 contents response.
6.3.2 Individual processes of fire development
In the following subclauses, we will discuss various components of fire development. The various processes are not
always in the same form as in the bus illustration in Figure 1. For example, the different heat transfer mechanisms
are listed in Figure 1 but not explicitly discussed here, because they are assumed to be general engineering
knowledge.
In some engineering tools like the zone models, descriptions of different component processes are compiled into a
single tool, making it possible to simulate the consequences of fire development. On many occasions, however, it is
possible to consider the processes independently to draw the necessary conclusions concerning the required safety
measures or the acceptability of a design.
6.3.2.1 Burning rate
The most important descriptor of a fire is the burning rate, which is quantitatively expressed as a heat release rate.
The burning rate may be calculated if the net heat flux to the surface and the latent heat of gasification are known.
Unfortunately, neither of them are easily obtained for practical materials, because the properties of the fuels are
time dependent and the net flux is affected by the flux from the flames of the burning item itself. The fuel vapours
block (absorb) the radiation transmitted from the flame, and typically only a small fraction of the energy released by
the flame can reach the surface. For horizontal pool fires, the net flux to the surface is only of the order of 1 % of the
total heat release rate.
Often the only reliable way to estimate the burning rate is to use experimental data. Oxygen consumption
calorimeters have been used to measure the burning rates of large-scale objects with rates of heat release of up to
[17]
tens of megawatts . Small-scale systems exist to measure the mass loss and heat release rates per unit area of
specimens under well defined conditions. By applying modelling techniques of varying complexity, it is then possible
to make reasonable estimates of the burning rates of larger objects, also under conditions differing from the
conditions under which the input data was obtained. Useful sets of information on the burning rates of materials and
products can be found in [10], [18] and [19].
Where it is not possible to characterize the combustible contents of the room of fire origin, fire growth is often
[20]
assumed to increase with the square of time using the relationship:
&
& 2
Q = (t/t ) (3)
Q
g
–2
& &
where the so-called growth time is the time to reach a heat release rate . Often in the literature = a.
t t
Q Q
g g
0 0
The value of a can be determined, in principle, based on statistical or experimental information on fire growth rates
in different occupancies. So far, experimental and statistical data are scarce, and engineering judgement is
therefore needed to determine the fire growth rate.
A parabolic fire is assumed to grow to a constant value when the fire becomes either fuel or ventilation limited. The
burning rates at later phases of fire development are discussed in 6.3.3 and 6.3.4.
Sometimes the fire growth rate can be expressed as an exponentially growing fire. In fact, a fire spreading upward
[21]
is more likely to grow exponentially than parabolically .
[22]
The idealised fire growth expressions have been criticised as being unrealistic . However, for design purposes,
when the exact type, location and geometry of the fire load is not known, no alternative approach has been
proposed.
© ISO
6.3.2.1.1 Input
Depending on the complexity of the model, the following input data are needed to estimate the burning rates of real
objects:
 thermal conductivity, specific heat capacity and density of the product;
 heat of gasification;
 heat of combustion;
 radiative fraction of rate of heat release (typically 30 %);
 mass loss rate or rate of heat release per unit area (from small-scale tests under a known exposure);
 mass loss rate and/or heat release rate (from large-scale tests on real objects).
6.3.2.1.2 Output
The output data from the burning-rate evaluation are:
 mass loss rate;
 heat release rate;
 surface regression rate.
6.3.2.2 Smouldering
For cellulosic fuels, smouldering typically yields more smoke and unburned species per unit mass of fuel than
flaming, but, because the fuel mass loss rate is low, the total-species generation rate is low. Smouldering may also
provide a pathway to flaming at a later stage of the fire.
Smouldering usually occurs in low-density organic materials. Smouldering may be initiated by self-ignition or by a
heat source embedded in the material or causing a heat flux at the appropriate level. A low heat flux may not be
sufficient to ignite a smouldering fire and a high flux may immediately cause a flaming fire.
In fire safety engineering, consideration of smouldering is needed if the generation of visible smoke and toxic
species is of interest at an ear
...

SLOVENSKI STANDARD
01-februar-2001
3RåDUQRLQåHQLUVWYRGHO=DþHWHNLQUD]YRMSRåDUDLQGLPQLKSOLQRY
Fire safety engineering -- Part 4: Initiation and development of fire and generation of fire
effluents
Ingénierie de la sécurité contre l'incendie -- Partie 4: Amorçage et développement des
feux et production des effluents du feu
Ta slovenski standard je istoveten z: ISO/TR 13387-4:1999
ICS:
13.220.01 Varstvo pred požarom na Protection against fire in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

TECHNICAL ISO/TR
REPORT 13387-4
First edition
1999-10-15
Fire safety engineering —
Part 4:
Initiation and development of fire and
generation of fire effluents
Ingénierie de la sécurité contre l'incendie —
Partie 4: Amorçage et développement des feux et production des effluents
du feu
A
Reference number
Contents
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Symbols and abbreviated terms .3
5 Subsystem 1 of the total design system .5
6 Subsystem 1 evaluations.5
6.1 General.5
6.2 Initiation of fire.6
6.3 Fire development .13
6.4 Smoke production .20
6.5 Species generation.23
7 Engineering methods .27
7.1 General.27
7.2 Estimation formulae .28
7.3 Computer models .28
7.4 Experimental methods .29
(informative)
Annex A Smoke measurement units .31
Bibliography.33
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet [e-mail]
Printed in Switzerland
ii
© ISO
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The main task of ISO technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
 type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
 type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
 type 3, when a technical committee has collected data of a different kind from that which is normally published
as an International Standard (“state of the art“, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until the data they provide are considered to be no longer valid or useful.
ISO/TR 13387-4, which is a Technical Report of type 2, was prepared by Technical Committee ISO/TC 92, Fire
safety, Subcommittee SC 4, Fire safety engineering.
It is one of eight parts which outlines important aspects which need to be considered in making a fundamental
approach to the provision of fire safety in buildings. The approach ignores any constraints which might apply as a
consequence of regulations or codes; following the approach will not, therefore, necessarily mean compliance with
national regulations.
ISO/TR 13387 consists of the following parts, under the general title Fire safety engineering:
 Part 1: Application of fire performance concepts to design objectives
 Part 2: Design fire scenarios and design fires
 Part 3: Assessment and verification of mathematical fire models
 Part 4: Initiation and development of fire and generation of fire effluents
 Part 5: Movement of fire effluents
 Part 6: Structural response and fire spread beyond the enclosure of origin
 Part 7: Detection, activation and suppression
 Part 8: Life safety — Occupant behaviour, location and condition
Annex A of this part of ISO/TR 13387 is for information only.
iii
© ISO
Introduction
Evaluation of the initiation and development of fire and the generation of smoke and toxic species is an essential
step in the fire safety design of buildings, processes, etc. These phenomena have been actively studied especially
during the last twenty years. Calculation methods and computer codes have been developed to make the
necessary evaluations. At the same time, advances in experimental techniques have made it possible to produce
input data for the calculation methods and to run large-scale tests for assessing the validity and limitations of the
models.
In most of the existing fire safety regulations, measures are taken to prevent the ignition of a fire by controlling the
use of materials and by controlling the amount and location of possible ignition sources. It is not, however, possible
to prevent all ignitions, and therefore measures are taken to control the fire development and the generation of
smoke and toxic species. In most of the existing building regulations, ignitability, flame spread, burning rate, smoke
production and toxic-species production are controlled by what are known as reaction-to-fire and flammability
classifications. These are to a great extent empirical and based on product performance in a specific small-scale
test. Similar regulations have been set on building contents, e.g. upholstered furniture, stored goods, etc., in some
countries.
A more modern approach for prescriptive regulations is to establish the classification scheme based on small-scale
tests in such a fashion that relative performance in one or more full-scale fire scenarios is replicated. If the
scenarios are sufficiently representative of real fire scenarios, the classification system becomes more reliable than
those based on performance in small-scale tests alone.
In this document, the initiation and development of fire and the generation of hazardous species is considered as
part of a global fire safety evaluation system. This part of ISO/TR 13387 is intended for use together with the other
parts as described in clause 6. For some applications, this part alone may be sufficient.
Clause 6 of this part of ISO/TR 13387 describes and provides guidance on the methods available to describe the
physical and chemical processes involved in:
 initiation of fire;
 fire development;
 smoke generation;
 toxic-species generation.
Clause 7 is a discussion of the engineering methods available to evaluate the initiation and development of fire and
the generation of smoke and gaseous species.
Quantitative information may be related to specific test conditions and/or specific commercial products, and thus the
application of data under different conditions may result in significant errors.
iv
TECHNICAL REPORT  © ISO ISO/TR 13387-4:1999(E)
Fire safety engineering —
Part 4:
Initiation and development of fire and generation of fire effluents
1 Scope
This part of ISO/TR 13387 is intended to provide guidance to designers, regulators and fire safety professionals on
the use of engineering methods for the prediction of the initiation of fire, the generation of fire effluents and the
development of fire inside the room of origin. It is not intended as a detailed design guide, but could be used as the
basis for the development of such a guide.
This part of ISO/TR 13387 provides a framework for critically reviewing the suitability of an engineering method for
assessing the potential for the initiation and development of fire and the generation of fire effluents. It also provides
guidance on the means to assess the effectiveness of fire safety measures meant to reduce the probability of
ignition, to control fire development and to reduce the accumulation of heat, smoke and toxic products or products
causing non-thermal damage. The methods for calculating the effects of design fires for use in the design and
assessment of fire safety of a building are also addressed.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this part of ISO/TR 13387. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this part of ISO/TR 13387 are encouraged to
investigate the possibility of applying the most recent additions of the normative documents indicated below. For
undated references, the latest addition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid international standards.
ISO 31-0:1992, Quantities and units — Part 0: General principles.
ISO 1000:1992, SI units and recommendations for the use of their multiples and certain other units.
ISO 5660-1:1993, Fire tests — Reaction to fire — Part 1: Rate of heat release from building products — (Cone
calorimeter method).
ISO 7345:1987, Thermal insulation — Physical quantities and definitions.
ISO 9705:1993, Fire tests — Full-scale room test for surface products.
ISO/TR 11696-1, Use of reaction to fire tests — Part 1: Application of results to predict fire performance of building
products by mathematical modelling.
ISO/TR 13387-1, Fire safety engineering — Part 1: Application of fire performance concepts to design objectives.
ISO/TR 13387-2, Fire safety engineering — Part 2: Design fire scenarios and design fires.
© ISO
ISO/TR 13387-3, Fire safety engineering — Part 3: Assessment and verification of mathematical fire models.
ISO/TR 13387-5, Fire safety engineering — Part 5: Movement of fire effluents.
ISO/TR 13387-6, Fire safety engineering — Part 6: Structural response and fire spread beyond the enclosure of
origin.
ISO/TR 13387-7, Fire safety engineering — Part 7: Detection, activation and suppression.
ISO/TR 13387-8, Fire safety engineering — Part 8: Life safety — Occupant behaviour, location and condition.
ISO 13571, Fire hazard analysis — Life-threatening components of fire.
ISO 13943, Fire safety — Vocabulary.
3 Terms and definitions
For the purposes of this part of ISO/TR 13387, the terms and definitions given in ISO 13943 and ISO/TR 13387-1
and the following apply.
3.1
emissivity
the ratio of the power per unit area radiated from a surface to that radiated from a black body at the same
temperature
3.2
extinction coefficient
a constant determining the decay of the light intensity in smoke per unit path length, given by K = (1/l) ln (I /I)
–1
It is expressed in m .
3.3
fire exposure
a process by which, or the extent to which, humans, animals, materials, products or assemblies are subjected to the
conditions created by a fire
3.4
heat flux
the rate at which heat crosses a surface per unit area of surface, expressed in W/m
In ISO 1000 and ISO 31-0, this is referred to as "density of heat flow rate".
3.5
heat of combustion
the energy which unit mass of material or product is capable of releasing by complete combustion, expressed in
J/kg
3.6
heat of gasification
the quantity of energy required to change a unit mass of material from condensed phase to vapour without change
of temperature, expressed in J/kg
3.7
ignition temperature
the minimum temperature measured on a material at which sustained combustion can be initiated under specific
test conditions, expressed in K
3.8
opening factor
1/2
A (h ) /A
v v T
© ISO
1/2
It is expressed in m .
For the meanings of the symbols, see clause 4.
3.9
pyrolysis
a process of simultaneous phase and chemical-species change caused by heat
3.10
smoke point
minimum height of a laminar axisymmetric diffusion flame (fuel volumetric mass loss rate) at which smoke escapes
from the tip of a flame, expressed in m
3.11
specific heat capacity
heat capacity divided by mass, expressed in J/(kg×K)
3.12
thermal conductivity
r
ratio of heat flux to temperature gradient, defined by the relation -·qk= ∇ T
It is expressed in W/(m×K).
3.13
thermal diffusivity
k
thermal conductivity divided by the density and the specific heat capacity, given by k = k/rc
It is expressed in m /s.
3.14
thermal inertia
the product of the thermal conductivity, the density and the specific heat capacity, given by
krc
2 4 2
It is equal to the square of thermal effusivity as defined in ISO 7345. It is expressed in J /(m ×K ×s).
3.15
total cross-sectional area of smoke
the average cross-sectional area of smoke particles perpendicular to the light path multiplied by the number of
smoke particles, expressed in m
3.16
ventilation factor
1/2
A (h )
v v
5/2
It is expressed in m .
For the meanings of the symbols, see clause 4.
4 Symbols and abbreviated terms
A area of an opening, expressed in m
v
A surface area of fuel, expressed in m
fuel
A floor area, expressed in m
F
A total area of the bounding surfaces in an enclosure, expressed in m
T
¢¢
© ISO
-2
–2
at , expressed in W×s&Q
g
1/2
F opening factor, expressed in m
5/2
F ventilation factor, expressed in m
V
f yield of species X, where X = CO, CO , etc.
X 2
g acceleration due to gravity, expressed in m/s
h height of an opening, expressed in m
v
I intensity of light after passing through smoke, expressed in W/m
I intensity of light in clean air, expressed in W/m
k thermal conductivity, expressed in W/(m×K)
–1
K extinction coefficient, expressed in m
kthermal diffusivity, expressed in W/(m×K)
l optical path length, expressed in m
L thickness of a specimen, expressed in m
m smoke density, expressed in dB/m
mass loss rate of fuel, expressed in kg/s&m
fuel
generation rate of species X, where X = CO, CO , etc., expressed in kg/s
m&X
N total number of smoke particles
–3
n number density of smoke particles, expressed in m
ffuel to air equivalence ratio
&Q heat release rate, expressed in W
2&heat release rate at the growth time in t fires, expressed in W; usually taken as 1 MW
Q
r
q heat flux (density of heat flow rate), expressed in W/m
&q external heat flux, expressed in W/m
ext
&q heat loss from the surface by convection or radiation, expressed in W/m
loss
rdensity, expressed in kg/m
seffective absorption cross-section of a smoke particle, expressed in m
T temperature, expressed in °C
T ignition temperature, expressed in °C
ig
T the lowest temperature at which a flammable mixture at its lean limit may burn, expressed in °C
L
T initial surface temperature, expressed in °C
¢¢
¢¢
¢¢
© ISO
T the lowest temperature at which a flammable mixture at its rich limit may burn, expressed in °C
U
t time, expressed in s
t growth time in a t fire, expressed in s
g
t time to ignition (ignition delay), expressed in s
ig
ttime constant, expressed in s
volume flow rate, expressed in m /s&V
f
V volumetric production rate of species X, where X = CO, CO , etc., expressed in m /s
X 2
x flame height, expressed in m
f
x position of pyrolysis front, expressed in m
p
5 Subsystem 1 of the total design system
The approach adopted in the work of ISO/TC 92/SC 4 is to consider the global objective of fire safety design. The
global design, described in more detail in ISO/TR 13387-1, is sub-divided into what are called "subsystems" of the
total design. A key principle is that inter-relation and interdependence of the various subsystems are appreciated,
and that the consequences of all the events in any one subsystem on all other subsystems are identified and
addressed. Another key principle is that the design is time-based to reflect the fact that real fires vary in severity and
extent with time. Ignition represents zero time.
In ISO/TR 13387-1, the total fire safety design is illustrated by an information bus analogy. The information bus has
three layers: global information, evaluation information and process information. In this information bus analogy,
subsystem 1 (SS1) concerns the initiation and development of fire and generation of fire effluent and is illustrated in
Figure 1. SS1 draws on other subsystems for the prescription or characterization of a fire and, in turn, provides
information for the other subsystems to employ. Definitions of terms concerning the global information bus are given
in ISO/TR 13387-1.
For example, SS1 provides the information on heat, smoke and species generation, which is then used by SS2 for
the calculation of smoke movement out of the room and in the building and by SS5 to assess evacuation and
rescue provisions. SS1 also calculates the temperature history in the enclosure of fire origin, which then is
employed by SS3 to predict the structural behaviour. The temperature and flow profiles in the room are employed
by SS4 to predict the detection of fire, as well as the activation of smoke control and suppression systems. The time
of activation of active control systems is then fed back by SS4 to SS1 for the prediction of subsequent fire
development and smoke and species generation. The initiation of a fire and its development outside the enclosure
of origin are also calculated by SS1.
The evaluations, and processes needed to do the evaluations, are discussed in detail in clause 6.
6 Subsystem 1 evaluations
6.1 General
In this clause, various fire phenomena and consequences of fire will be discussed. The required input information
and the possible output information will be identified. Areas for which shortages in engineering methods and lack of
knowledge are known to exist will be addressed. The text makes reference to existing acknowledged literature,
whenever such is available.
© ISO
6.2 Initiation of fire
6.2.1 Evaluation of initiation of fire
In deterministic fire safety engineering design, ignition is often simply assumed to occur and no calculations on the
ignition process are performed. In other instances, especially when the combustible contents and the distribution of
ignition sources in the room of fire origin are known, performing calculations on the ignition process can provide
valuable information on the possible fire development in the room. Evaluation of ignition is needed especially when
the fire safety engineer has to evaluate whether one product can be replaced by another, all other design
parameters being fixed. Often the task is to consider if a potential ignition source is likely to cause ignition of
adjacent items, i.e. if the first item ignited will cause a second item to be ignited, and thereby the fire to spread to a
hazardous extent.
© ISO
Figure 1 — Illustration of the global information, evaluation and process buses for SS1
© ISO
The probability of ignition is a subset of design fires which is addressed in ISO/TR 13387-2. Assessment of the
probability of ignition is needed when making decisions about the design fire scenarios and event trees used in risk
assessment. Probabilistic design and risk assessment are discussed in more detail in ISO/TR 13387-1.
This subclause discusses ignition of items which are in one way or another exposed to heating from an external
source. This source of heat can be of various intensities and shapes, varying from (say) a match flame to an
actively burning fuel package. Fire development as discussed in 6.3 can be considered to be a series of non-
simultaneous ignitions, each of which generally behaves in the theoretical manner discussed herein.
Figure 2 identifies parameters having an influence on the ignition of various kinds of fuel. A condition for ignition is
that both a flammable substance and an ignition source exist. The flammable substance may appear in a number of
different forms. The heat transfer from the ignition source to the flammable substance may also take different forms,
the processes being, in addition, sensitive to the local environment around the source and the exposed substance.
6.2.1.1 Input
The evaluation of the initiation of a fire (see Figure 1) requires as input information from the global information the
following:
 building parameters (e.g. lining materials, their thermal and chemical properties, their location with respect to
heat sources);
 fire loads (building contents, thermal and chemical properties of building contents, location with respect to heat
sources);
 fire scenarios (properties of ignition sources, their number and their locations);
 thermal profile (radiative, conductive and convective heat fluxes, gas temperature, initial fuel temperature);
 size of fire/extent of smoke (area exposed to a burning fire).
NOTE This information is also needed for evaluating the ignition of second, etc., items. Therefore, e.g. the size of
fire/extent of smoke is an input or output, depending on when it is used during an evaluation.
6.2.1.2 Output
The evaluation of the initiation of a fire (see Figure 1) provides the following information to the global information:
 fire scenarios (object first ignited, time to ignition);
 size of fire/ extent of smoke (area first ignited, size of initial flame).
6.2.2 Gas phase ignition
The process of ignition to give flames requires mixtures of gas phase combustibles at an appropriate fuel-to-air ratio
and either local temperature fields higher than the auto-ignition limit or a pilot source. The necessary conditions for
any gaseous mixture of fuel are usually expressed as ignitability regions as in Figure 3. If a fuel is not naturally in
the gas phase, energy must be applied to the substance to bring it to the gaseous state. For liquids, the amount of
energy required depends on the vaporisation rate and the way in which the liquid is distributed or the material upon
which the liquid is absorbed, i.e. bulk liquids will not ignite until the bulk temperature equals or exceeds the flash
point. If the liquid is atomised, its ignition propensity will approach the ignitability of gaseous mixtures of the same
material, depending on the degree of atomisation and the temperature of the environment. If the liquid is absorbed
in a porous medium, the energy demand for ignition will depend on how fast the porous material will absorb energy
and heat up. In this case, the thermal properties of the porous medium will dominate the process.
In the case of gaseous or liquid fuels, the engineering task is usually to consider whether a flammable mixture can
be created in the space of concern. In the case of solids, the task can usually be reduced to evaluating whether the
surface temperature will become high enough to cause ignition, and no gas phase considerations are needed as we
can see in 6.2.3.
© ISO
Figure 2 — Factors to be taken into account when assessing ignition potential
© ISO
Figure 3 — Effect of temperature on the limits of flammability of a flammable vapour/air mixture at constant
[1]
initial pressure
Useful information on gas phase ignition can be found in references [1] and [2].
6.2.2.1 Input
The evaluation of gas phase ignition may require, as input, specific information on the following processes and
product properties:
 fuel properties, e.g. latent heat of gasification, flash point, flammability limits, vaporisation or pyrolysis rate at
defined temperatures and thermal-exposure histories;
 radiative, convective and conductive heat transfer to the surfaces to estimate the fuel flow rate and the thermal
conditions in the space of interest;
 fuel/air mixing, e.g. the air flow in the space to estimate the dilution of the gaseous fuel;
 properties of potential ignition sources, e.g. temperature and spark energy.
Detailed discussions of the flammability of gas mixtures and ignition of liquid fuels, as well as tabulations of fuel
[3]
properties, can be found in various publications, e.g. the SFPE Handbook .
6.2.2.2 Output
The output of the evaluation is the time to ignition or whether ignition will occur at all.
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6.2.3 Ignition model for solids
Because most accidental fires in buildings are initiated on solid materials, this subclause is restricted to surveying
the parameters that dominate the ignition of materials in the solid phase.
Heat transferred from a source to a target results in a rise in the temperature of the target. The conditions for
ignition are produced when pyrolyzates from the target mix with air to produce ignitable mixtures at temperatures
that could locally exceed spontaneous-ignition temperatures. The presence of any kind of pilot source will generally
cause ignition as soon as the fuel/air ratio permits. Factors that control this process are the mode of ignition, the
rate of heat transfer from the source, the target composition, the target location, the thermal and optical properties
of the target and the availability of air. For common ignition sources (hot object, intense electric arc, smouldering
material or flame), two types of ignition are possible: (1) glowing ignition (exothermic reaction at the surface of a
material with air) and (2) flaming ignition (ignition that occurs in the gas phase mixture of pyrolyzates and air).
Materials that ignite to glowing ignition may smoulder (combustion that occurs and propagates in the bulk material)
for some period. If conditions are appropriate, smouldering may undergo a transition to flaming ignition and rapid fire
spread. Materials that are ignited to flaming ignition may sustain the flaming mode and, if conditions are right, may
spread to a larger size. Conversely, if the ignition experience is short, the flaming mode may be transient, and either
convert to glowing or smouldering, or simply self-extinguish. As with the ignition process, the transient or sustained
behaviour of the post-ignition condition is controlled by the composition and constitution of the material.
Regardless of ignition source, the response of a material to heating is dominated by the physical properties of the
material. A detailed discussion of the ignition of solids can be found in reference [4]. Useful information can also be
found in [5] and [6]. ISO/TC92/SC1 is working on a document describing the theoretical background of the ISO
reaction-to-fire tests (ISO/TR 11696-1). The document includes a discussion of ignition under radiant heat
exposure.
The thermal theory of ignition assumes that each material can be characterised by a critical ignition temperature
[7]
T . By using simple heat-conduction theory, one can show that, for thermally thick material behaviour, the ignition
ig
delay is given by:
2 2
t ∝ krc(T – T ) /(&q – &q ) (1)
ig ig 0 ext loss
For thermally thin material behaviour, i.e. if the temperature in the material is approximately uniform, the ignition
delay is given by:
t ∝ rcL(T – T )/(&q – &q ) (2)
ig ig 0 ext loss
The loss term &q contains all the losses by re-radiation and convection.
loss
The product property term krc(T – T ) or rcL(T – T ) can be determined experimentally. This parameter has also
ig 0 ig 0
[8],[9]
been called a flux time product (FTP) , and the square root of the parameter a thermal-response parameter
[10]
(TRP) .
When deriving the equations above, all the properties have been taken as constants. In reality, the properties
depend on temperature and other ambient conditions. For example, under slow heating the surface may pyrolyze
sufficiently for the chemical properties to change, thus changing e.g. the ignition temperature. Usually, the
experimental data available is from tests with a pilot ignition source. Without a pilot flame, the critical ignition
temperature is considerably higher.
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It may also be difficult to know whether the product is thermally thin or thick. The condition L >> (k t ) is widely
ig
used for characterising products with thermally thick behaviour. Another practical rule of thumb is that a product is
considered to show thermally thick behaviour if the physical thickness L is > 0,6r&q , where L is in mm, the density
ext
3 2 [8]
r in kg/m and the heat flux &q in kW/m .
ext
The loss term depends on the ambient conditions, specimen size and orientation, etc. For example, different&q
loss
convective cooling of the surface may significantly influence the ignition delay time. One must therefore be very
careful when applying the numerical data obtained even in standardised tests like the ISO ignitability test or the
cone calorimeter. Proper corrections can be made if the conditions are sufficiently well defined.
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At ignition, the loss term (&q ) is equal to the critical heat flux for ignition. This is derived by extrapolation from a
loss
limited number of tests at different levels of radiant heat flux. However, the true minimum heat flux for ignition may
be lower or higher because of the changes in the physical and chemical properties of the surface under extended
exposure. The significance of this discrepancy depends to a great extent on the application of the data.
Special attention has to be given if the product under consideration melts. Some polymers that have low melting
temperatures will melt away from moderate- to low-intensity ignition sources before the target attains its ignition
temperature. It is therefore possible that product information based on some standard tests may not guarantee low
flammability; under a higher exposure, the product may ignite easily.
The critical flux for ignition and the effective ignition temperature may be influenced by adding fire retardants to the
solid. For some fire retardants, the effect may be to decrease the time to ignition under specific conditions. The
benefit of the retardants is seen as a reduced burning rate.
In the above discussion, the intensity of the radiant source was assumed adequate to positively ignite a target.
Normally, pure radiant sources would not cause the primary ignition in an accidental fire sequence. However, fire
spread from an initially ignited item may occur by means of radiant heat transfer. Factors that define the radiant
intensity of a source fire are flame area and thickness. The flame volume determines the flame emissivity, which is
a number between 0 and 1. For hydrocarbon fuels, flames thicker than 1 m will generally have an emissivity
approaching 1. This factor dictates the efficiency with which radiant energy is transferred between source and
target. The flame size, along with the distance and angular intercepts between source and target, determines the
view factor, which is also a number between 0 and 1.
View factors for various ideal shapes of hot objects can be found in reference [11]. Very often, flames from pool fires
are treated as radiating cylinders the height of which depends on the burning rate or the heat release rate.
Flame size for most fuels is directly proportional to the mass burning rate or heat release rate. Correlation can then
[12]
be created to enable the calculation of the minimum safe distance from a burning item .
6.2.3.1 Input
The evaluation of the ignitability of solids may require, as input, specific information on the following processes and
product properties:
 fuel properties (thickness, surface emissivity, thermal conductivity, density, specific heat capacity, ignition
temperature under various conditions, critical radiant flux for piloted ignition);
 radiative, convective and conductive heat transfer to the surfaces to estimate the fuel flow rate and the thermal
conditions in the space of interest;
 properties of potential ignition sources, e.g. temperature and spark energy, size of flame.
6.2.3.2 Output
The output of the evaluation may be either the time to ignition or whether ignition is possible at all.
6.2.4 Ignition to smouldering
Materials which are prone to smouldering have particular chemical compositions, form char on decomposition and
are generally low density (e.g. flexible polyurethane foams, cotton batting and pulverized-paper insulation). Contact
with ignition sources such as cigarettes or hot surfaces can result in ignition which, if sustained, will propagate as
smouldering combustion.
For cellulosic materials, the initiation of smouldering requires that the cellulose be converted to char, and this can
[13]
occur after prolonged exposure to temperatures above 100 °C .
The same requirements have to be met for smouldering ignition of synthetic polymers to occur. In addition, these
materials require a prolonged, low-intensity ignition source. Note that many of the conditions that promote
smouldering combustion are similar to those necessary for self-ignition and spontaneous combustion, i.e. a material
that is susceptible to oxidation, and an environment where the heat generated by oxidation is contained by a
medium of low heat loss potential. Self-heating parameters are summarised succinctly in reference [14] and
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exhaustively in [15]. Many other sources of useful information on the assessment of self-ignition potential are
available.
In the literature, the input data needed for evaluation of smouldering ignition is scarce. The self-ignition propensity is
usually evaluated by a series of small-scale tests from which parameters are derived to enable evaluation of the
critical storage temperature of a larger volume of the same product. The scaling laws are based on fundamental
theory, and the extrapolation to larger scale has turned out to be remarkably reliable in a great number of
applications.
6.3 Fire development
6.3.1 Evaluation of fire development
Evaluation of fire development is closely linked to the quantification of a design fire discussed in detail in
ISO/TR 13387-2. There are basically two distinctly different methods of determining the design fire for a given
scenario. One is based on knowledge of the amount, type and distribution of combustible materials in the
compartment of fire origin. The other is based on knowledge of the type of occupancy, where very little is known
about the details of the fire load.
The design fire and the fire development are usually quantified by the heat release rate (HRR) as a function of time.
Once the heat release rate is known, the flame height and the gas temperatures in the room can be estimated using
methods discussed later in this subclause. The external heating of a second object can then be calculated. The
development of the fire can then be considered to be a sequence of non-simultaneous ignitions, which generally
behave in the theoretical manner discussed in 7.1. A design fire can therefore be arrived at, using data from
experiments to estimate the heat release rate and using methods outlined in 7.1 for calculating the time to ignition.
In some cases, more detailed methods can be used to simulate fire development. These may be needed especially
when evaluating the relative fire safety of products in a specific application. Guidance on models of this kind will be
given in the following subclauses describing the processes of fire development. It should, however, be noted that for
design purposes the need for accurate data is not as high as for predicting the results of a single experiment. One
may never cover all the possible fire situations and, therefore, characteristic data based on statistical data for a
given occupancy must be applied.
Reference [16] provides a useful discussion about modelling fire growth from ignition to full involvement.
6.3.1.1 Input
The evaluation of the development of a fire (see Figure 1) requires as input information the following:
 building parameters (e.g. lining materials, thermal and chemical properties, location);
 fire loads (building contents, thermal and chemical properties of building contents, location);
 fire scenarios (e.g. experimentally determined characteristics of the first item ignited);
 thermal profile (radiative, conductive and convective heat fluxes, gas temperature, initial fuel temperature);
 building condition (conditions of the building products, e.g. due to pre-heating);
 contents condition (conditions of the building contents, e.g. due to pre-heating).
6.3.1.2 Output
The output data are:
 Size of fire/smoke (e.g. burning area, flame height, heat release rate, mass loss rate, smoke density in the
room);
 thermal profile (temperature and heat flux distribution in the room of origin);
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 pressure/velocity profile (e.g. pressure at smoke vents, flow through vents, velocity in the ceiling jet);
 building response;
 contents response.
6.3.2 Individual processes of fire development
In the following subclauses, we will discuss various components of fire development. The various processes are not
always in the same form as in the bus illustration in Figure 1. For example, the different heat transfer mechanisms
are listed in Figure 1 but not explicitly discussed here, because they are assumed to be general engineering
knowledge.
In some engineering tools like the zone models, descriptions of different component processes are compiled into a
single tool, making it possible to simulate the consequences of fire development. On many occasions, however, it is
possible to consider the processes independently to draw the necessary conclusions concerning the required safety
measures or the acceptability of a design.
6.3.2.1 Burning rate
The most important descriptor of a fire is the burning rate, which is quantitatively expressed as a heat release rate.
The burning rate may be calculated if the net heat flux to the surface and the latent heat of gasification are known.
Unfortunately, neither of them are easily obtained for practical materials, because the properties of the fuels are
time dependent and the net flux is affected by the flux from the flames of the burning item itself. The fuel vapours
block (absorb) the radiation transmitted from the flame, and typically only a small fraction of the energy released by
the flame can reach the surface. For horizontal pool fires, the net flux to the surface is only of the order of 1 % of the
total heat release rate.
Often the only reliable way to estimate the burning rate is to use experimental data. Oxygen consumption
calorimeters have been used to measure the burning rates of large-scale objects with rates of heat release of up to
[17]
tens of megawatts . Small-scale systems exist to measure the mass loss and heat release rates per unit area of
specimens under well defined conditions. By applying modelling techniques of varying complexity, it is then possible
to make reasonable estimates of the burning rates of larger objects, also under conditions differing from the
conditions under which the input data was obtained. Useful sets of information on the burning rates of materials and
products can be found in [10], [18] and [19].
Where it is not possible to characterize the combustible contents of the room of fire origin, fire growth is often
[20]
assumed to increase with the square of time using the relationship:
&&2
Q = (t/t ) (3)
Q
g
–2&&where the so-called growth time is the time to reach a heat release rate . Often in the literature = a.
t t
Q Q
g g
0 0
The value of a can be determined, in principle, based on statistical or experimental information on fire growth rates
in different occupancies. So far, experimental and statistical data are scarce, and engineering judgement is
therefore needed to determine the fire growth rate.
A parabolic fire is assumed to grow to a constant value when the fire becomes either fuel or ventilation limited. The
burning rates at later phases of fire development are discussed in 6.3.3 and 6.3.4.
Sometimes the fire growth rate can be expressed as an exponentially growing fire. In fact, a fire spreading upward
[21]
is more likely to grow exponentially than parabolically .
[22]
The idealised fire growth expressions have been criticised as being unrealistic . However, for design purposes,
when the exact type, location and geometry of the fire load is not known, no alternative approach has been
proposed.
© ISO
6.3.2.1.1 Input
Depending on the complexity of the model, the following input data are needed to estimate the burning rates of real
objects:
...