ISO/TR 17252:2019

TECHNICAL ISO/TR
REPORT 17252
Second edition
2019-05
Fire tests — Applicability of reaction
to fire tests to fire modelling and fire
safety engineering
Essais au feu — Applicabilité des résultats de l'essai de réaction au feu
aux techniques de modélisation et de sécurité contre l'incendie
Reference number
ISO/TR 17252:2019(E)
©
ISO 2019

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ISO/TR 17252:2019(E)

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ISO/TR 17252:2019(E)

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 1
5 Fire initiation and growth . 2
5.1 Specification of fires and fire scenarios . 2
5.1.1 Background. 2
5.1.2 Design fire types . 3
5.2 Sensitivity analysis in the design process . 5
5.3 Limits of applicability . 6
6 Sources and type of data for input into design . 6
6.1 Type of data for input into design . 6
6.2 Complexity of the modelling approach with regard to input data . 6
6.3 Using ISO/TC 92/SC 1 derived reaction-to-fire tests parameters in models for FSE . 9
7 Application of test results and limits of applicability .11
7.1 Limiting factors affecting experimental quantification of fire growth .11
7.2 Repeatability and reproducibility.11
7.3 Heat flux measurements .11
7.4 Ignition .12
7.5 Flame spread .12
7.6 Heat release rate .12
7.7 Smoke production rate .12
7.8 Differences between testing conditions and real fire scenarios .13
7.9 Limitations of generalizing product behaviour .14
Annex A (informative) Review of fire test standards .15
Bibliography .31
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ISO/TR 17252:2019(E)

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 procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www. iso. org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www. iso.o rg/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www. iso
.org/iso/foreword. html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 1, Fire
initiation and growth.
This second edition cancels and replaces the first edition (ISO/TR 17252:2008), which has been
technically revised. The main changes compared with the previous edition are as follows:
— The title of Clause 5 was changed;
— Former subclauses 5.1.1 and 5.1.2 have been merged into 5.1;
— New subclause 5.2 has been added: “Quantitative definition of fires and fire scenarios”;
— Clause 6 has been re-written, the title has been changed to “Sources and types of input data for fire
safety engineering”, subclauses 6.2 and 6.3 have been added;
— Clause 7 has been re-written, the subclauses have been re-arranged and text has been added;
— Clause 8 has been integrated in Clause 7 and totally changed, the title also has been changed to
“Limitations of generalizing product behavior”;
— Annex A has been re-written, tests have been added, description of the tests has been compressed
with more focus on FSE.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www. iso. org/members. html.
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ISO/TR 17252:2019(E)

Introduction
There is a current trend towards performance-based approaches in national building regulations.
This trend has seen rapid advancement internationally in the development of fire safety engineering.
This has been supported by the application of fire modelling over the last 15 years, as marked by the
1)
originally published ISO/TR 13387-1 to 8 , and followed by ISO 23932-1, ISO/TS 16733, ISO 16730, ISO/
TS 24679 and ISO/TR 16738. The impact of these documents and activities carried out nationally, have
clearly identified that there are inconsistencies between the requirements of fire safety engineering
(including the application of fire modelling) and the data reported from standard fire tests and ad hoc
experiments.
The document is intended to assist in the development of an internationally consistent approach to
support fire safety engineering activities by appropriate fire test methods that, where possible, are also
used for the primary function of fire safety regulation of the use of construction products.
It examines the majority of the current reaction to fire test methods in the TC 92/SC 1 portfolio and
provides information to support the use of the data that the tests provide for fire safety engineering
and fire modelling.
1) The ISO/TR 13387 series is withdrawn.
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TECHNICAL REPORT ISO/TR 17252:2019(E)
Fire tests — Applicability of reaction to fire tests to fire
modelling and fire safety engineering
1 Scope
This document gives guidelines on the applicability of the existing reaction to fire tests to fire safety
engineering and fire modelling. It also gives general guidance on the type of data needed for fire safety
engineering calculations and for fire modelling.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
— IEC Electropedia: available at http: //www .electropedia .org/
3.1
design fire
quantitative description of assumed fire characteristics within the design fire scenario
3.2
design fire scenario
specific fire scenario on which an analysis will be conducted
3.3
fire scenario
qualitative description of the course of a fire with time, identifying key events that characterise a
particular fire and differentiate it from other possible fires
4 Symbols and abbreviated terms
FSE Fire safety engineering
t is the characteristic time from reference ignition to reach heat release rate Q (s)
g 0
is heat release rate (MW)

Q
is the reference heat release rate, often taken to be 1 MW

Q
0
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5 Fire initiation and growth
5.1 Specification of fires and fire scenarios
5.1.1 Background
Design fire scenarios are at the core of the fire safety engineering methodology described in
ISO 23932-1, ISO/TS 16733, ISO 16730-1, ISO 24679-1 and ISO/TR 16738. An additional series of
standards: ISO 16734, ISO 16736, ISO 16737 and ISO 16732-1, extend and implement these concepts.
The methodology is based upon analysing particular design fire scenarios and then drawing inferences
from the results with regard to the adequacy of the proposed fire safety system to meet the performance
criteria that have been defined. Identification of the appropriate scenarios requiring analysis is crucial
to the attainment of a building that fulfils the fire safety performance objectives.
The characterisation of a design fire scenario for analysis purposes should involve a description of such
things as fire initiation, growth and extinction of fire, together with the likely smoke and fire spread
routes under a defined set of conditions. This may include consideration of such conditions as different
combinations of outcomes or events of different fire safety subsystems, different internal ventilation
conditions and different external environmental conditions. The consequences of each design fire
scenario should be considered. For example, it is important to realise that smouldering fires may have
the potential to cause a large number of fatalities in certain occupancies such as residential buildings
although there is no reaction-to-fire test in the TC 92/SC 1 portfolio which covers smouldering
conditions.
Examples of typical design fire scenarios include:
— Room fire (corner, ceiling, wall, floor);
— Fires in corridors and stairwells;
— Single burning item fire (furniture, waste paper basket, fittings);
— Developing fire;
— Cable tray or duct fire;
— Roof fires (underside);
— Cavity fire (wall, floor, façade, plenum);
— Fire in transport vehicles;
— Arson
1) Internal
2) External;
— Fire in neighbouring building;
— Fire in external fuel packages;
— Fire on roof and flying brands from adjacent buildings;
— Fire on façade;
— Subterranean fires;
— Forest fires or wild fires;
— Fire in tunnels and underground facilities.
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Following identification of the relevant design fire scenarios, it is necessary to describe the assumed
characteristics of the fire on which the design will be based. A combination of fire characteristics is
used to define the design fire and usually requires quantification of the following variables with respect
to time:
— Heat release rate [HRR (peak, mean, total, etc.)];
— Toxic species production rate;
— Smoke production rate (SPR);
— Fire size (including flame length);
— Time to key events such as flashover;
— Other factors such as temperature, emissivity and location may also be required.
The fire characteristics listed above, are influenced by a number of factors which include:
— type, size and location(s) of ignition source;
— ignitability of fuel;
— distribution and type(s) of fuel (with material related parameters as heat of combustion, combustion
efficiency);
— fire load density;
— rate of heat release characteristics;
— geometry of enclosure;
— exposed surface area;
— status of doors and/or windows (open or closed);
— internal ventilation conditions (e.g. building air handling system);
— external environmental conditions (e.g. outside temperature, wind velocity and directions);
— external heat flux.
Additionally, events that happen during the fire can modify the design fire and these are typically
accounted for in a fire safety engineering approach to design. For example, the breakage of a window
will alter the ventilation conditions and will influence the design fire. The incorporation of active fire
protection measures into a design will also impact upon the design fire. It is therefore important that
the effects changes in ventilation, of suppression systems, smoke control systems and intervention by
the fire service are considered when appropriate.
5.1.2 Design fire types
For design purposes, often an estimate of the heat release rate of the fire or the temperature rise in
the room as function of time is used. The design fire curves represent an idealization of a real fire that
might occur, and there is a great variety in the way they are mathematically expressed. For example, the
design fire curves used for tunnels include different types of fire growth rates, including, linear growth,
quadratic growth or exponential etc. Typical fire curves are given for instance in ISO 834-1, Eurocode 1,
EN 13501-2 or ISO/TS 3814, where heat release rate, Q, growth in design fires is often characterized in
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ISO/TR 17252:2019(E)

terms of exponential or power-law rate of time, t, from the reference ignition time. The most commonly
used relationship for these models is the t-squared fire given by:
2

QQ= tt/ (1)
()
0 g
Where time, t, is measured from the reference ignition time, and the growth time t is the time from the
g
reference ignition time to reach heat release rate Q .
0
For design of more realistic fires, the fire growth functions can be combined with a maximum HRR value
[33][34]
and a decay function to resemble abatement . However, in building fire safety design, usually the
growth rate alone, e.g. Formula (1) is considered when growing fires are the unique fire scenario to be
dealt with, whereas in other specific applications, such as in tunnel fires, the entire fire curve may be
considered. Using different types of growth and decay rates combined with maximum HRR profiles as
peak values or plateau periods means that the curve has to be represented mathematically for different
time periods. Figure 1 gives examples of different design fire types including the growth phase, a
constant phase on a maximum level and a decay phase. Three different curves (1, 2 and 3) are given as
heat release rate versus time. All three fires are assumed to have a growth phase following a t-square
relation and then a phase of constant maximum heat release rate and then a decay phase. The constant
phase of the maximum level can be reduced to 0 s. In this case the design fire may have a triangular
shape. Curve 4 shows a steeper increase in the heat release rate in the beginning which can represent
circumstances where the fire develops faster than in other design scenarios.
Figure 1 — Examples for different design fire types (curves 1, 2, 3 and 4)
In addition, when the fuel package for a particular design fire scenario is well defined and unlikely
to change significantly during the life of the building, the actual burning characteristics of the fuel
package can be used as the design fire. In such cases, oxygen consumption calorimetry, for example,
ISO 9705-1 is useful for providing quantitative data.
Because of the growing complexity of buildings or other enclosures of interest, and the very different
nature of fires associated with such places, it is not always possible or desirable to use a given heat
release rate or temperature-time curve. In some cases, the fire spread through the building or enclosure
might be important and cannot be predicted easily. In other cases, a fire which already occurred is to be
investigated. Moreover, the materials involved in fire (e.g. property, facades, ducts, ceilings etc.) inside
a building/enclosure respond differently and in a complex manner to the fire scenarios, in comparison
to a mathematical design fire. Therefore, in such cases, it is not always possible nor desirable to use
a design fire size a as input to the calculations. In many such cases, it may be preferable to use the
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geometry of the building or enclosure, provide material pyrolysis properties, and use the initial fire
load as an input for computational fluid dynamics (CFD) model simulations/calculations. CFD models
are field models which solve the balances of mass, momentum and energy either in sub volumes or on a
numerical grid of the computational domain. CFD models on fire usually include additional models for
radiation, turbulence, chemical reactions as well as material pyrolysis to solve the balances. The set of
equations can only be solved numerically through various software platforms. Such CFD fire modelling
codes require material properties to model the pyrolysis of the materials which are involved in the fire.
For CFD applications, different pyrolysis models can be used and combined with CFD models to predict
[33]
the material pyrolysis behaviour, some of which have been applied recently in similar applications
[34][35][36].
In some cases, it is now possible to predict the fire growth behaviour using calculation and modelling
methods. For such approaches, the validation and verification of the approach will be an important
consideration and will be dependent upon the quality and reliability of the input data, whether it is
generated from test methods or material data. This is described in more detail in section “sources of
data for input into design”.
As a result of the calculations the fire development with its consequences regarding the production and
spread of smoke and toxic gases might be used to assess the hazard of different situations which is not
further discussed here.
5.2 Sensitivity analysis in the design process
The design fire characteristics will have a major impact upon many aspects of the design since they
form the inputs into many of the deterministic quantitative design calculations carried out during a
fire safety engineering analysis. A sensitivity analysis can be defined as the calculation of changes in
outputs for variations in an input parameter of interest. It may be possible to deal with the uncertainties
associated with the deterministic design by taking a conservative approach. However, the judgement of
conservatism is very subjective. A worst-case design fire in terms of maximum size or growth rate will
typically also be the worst case for determination of the:
— Effect of smoke control systems on the fire scenario;
— Effect of suppression systems on fire growth;
— Time to structural failure;
— Time and extent of fire spread within and from enclosure;
— Fire service extinguishing capacity.
However, the same design fire may represent a best-case scenario for:
— Time of activation of alarm system;
— Time of activation of smoke control systems;
— Time of activation of smoke and fire barriers;
— Time of activation of suppression systems.
It is therefore recommended that a sensitivity study be carried out on the consequences of the choice of
design fire on the different parts of the quantitative assessment.
The objective of a sensitivity study is to establish the impact on the output parameter(s) caused by
variation in the input parameter(s). It is not intended to check the accuracy of the results.
If a single assumption is shown to be critical to the design and potentially the level of safety,
consideration should be given to providing a degree of redundancy in the design or to carrying out a
further, perhaps probabilistic study related to that assumption.
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5.3 Limits of applicability
Application of empirically-based calculation methods and other types of approach to fire safety
engineered design, e.g. zone or CFD models, are generally assumed to be adequate provided that the
approaches are used within their stated limits of applicability. However, these limits are not always
stated and therefore it is incumbent upon the user to determine what these are for each method applied.
If an approach is used outside of its limits of applicability, it is important that it is assessed from a
theoretical basis and/or by comparison with experimental data. In such cases, it is usual to include
some suitable safety factors in the analysis.
6 Sources and type of data for input into design
6.1 Type of data for input into design
In performance-based fire safety engineering, calculation methods are used that need data for the fire
[1][2][3]
performance of various materials or components . The performance data can be obtained from
several ISO international standards test methods, currently in use. In these tests, relatively simple
measurements are made to estimate various aspects of the relative fire performance of the materials
at each stage of a fire and thereby better understand hazards that might be associated with use of that
material should a fire occur.
There are a limited number of ISO international standards test methods that specify apparatus capable
of providing quantitative data for the fire parameters of materials and products which can be utilized
in the predictive models for the assessment of fire hazards. Some of these standards and their outputs
are presented in Table 2, below. Depending on the complexity of a model, the set of required input
parameters will vary. However, the fire parameters as used in ISO 16730-1 and presented in Table 1
may be measured in ISO 5658-2, ISO 5657 (q′′ , T , T , kρc, Φ), ISO 5660-1 and ISO 12136 (q′′ , T ,
ig s,min ig
cr cr
kρc, ΔH , ΔH , E/A).
eff g
Table 1 — Fire parameters obtained in ISO international standards test methods
ISO T TRP HRR ΔH Q / χ RHR

ig eff PCS E/A
′′
m
q
cr
interna- Q
PCI
12/
tional
kcρ ΔT
()
ig
standard
2 1/2 2
a
(kW/m ) (K) (kW-s / (kW) (kJ/ g) (MJ/ (kW/m ) (kg/s) (kJ/g)
number
(MJ/m2)
2
m ) kg)
12136 X X X X X X X X X X
5660-1 X X X X X X X X X
5658-2 X X
14696 X X X X X X X X X
5657 X X X
1716 X
9239-1 X
9705-1 X X
24473 X X X X
a
ISO 12136 Fire Propagation Apparatus, ISO 5660-1 Cone Calorimeter test, ISO 5658-2 Spread of flame test, ISO 14696
ICAL test, ISO 5657 Ignitability test, ISO 1716 Bomb Calorimeter test, ISO 9239-1 Flooring Radiant Panel test, ISO 9705-1
Room corner test, ISO 24473 Open Calorimetry test.
NOTE  Critical heat flux measured in ISO 9239-1 is not appropriate for modelling purposes.
6.2 Complexity of the modelling approach with regard to input data
One relatively simple approach to simulate a fire is to define the heat release of the fire (often varying
2
over time) as presented earlier in the document. One example of this approach is the t -curve,
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Formula (1). This approach represents an educated guess of the fire (fire size and development) which
might occur in a building, transport vehicle or tunnel. The influence of the given fire on the structure or
with respect to tenability criteria is then investigated.
In this document, we intend to identify ISO international standards fire test outputs that can be used in
fire safety engineering calculations to predict the performance of materials in a realistic fire scenario.
For example, there are several models developed by various researchers in order to predict the
performance of materials in an ISO 9705-1 room corner scenario using as input the fire performance
data derived from several ISO international standards test methods. Most widely used fire safety
[4][9][11][13][18][19]
engineering models are based on utilizing data from small-scale fire tests to predict
heat release rate (HRR) and flashover in the ISO 9705-1 room corner test (US versions are ASTM E2257
and NFPA 265). In these models, the predicted output of the room corner test is the time to flashover,
[6]
defined as the time taken for the fire to reach a size of 1 000 kW (HRR). Other engineering models
[7][10][12][13][14][15][16][17][19]
have been used in attempts to predict flame spread behaviour based on
fire performance data measured using various ISO international standards test methods. These data
include ignition temperature, ignition time, critical heat flux for ignition, thermal inertia, heat release
and mass loss rates, effective heat of combustion and gasification, total energy per unit area, etc. It
should be pointed out that using such measurements as input data for these modelling calculations is
expected to provide tools to predict flame spread behaviour of products only for conditions similar
to those used in the test. Such scaling laws and models might not work for other fire scenarios and
conditions. ISO/TR 17252 provides guidelines for limits for applicability.
The following are some examples of predictive models for the fire behaviour of interior finish materials
of buildings:
[6]
a) Karlsson Magnusson model ;
[7]
b) Wickstrom-Goransson model ;
[10]
...