Fire safety engineering -- Part 6: Structural response and fire spread beyond the enclosure of origin

Ingénierie de la sécurité contre l'incendie -- Partie 6: Réponse structurelle et propagation du feu au delà de l'enceinte d'origine

Požarno inženirstvo - 6. del: Odziv konstrukcije in širjenje požara izven prostora nastanka požara

General Information

Status
Published
Publication Date
31-Jan-2001
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Feb-2001
Due Date
01-Feb-2001
Completion Date
01-Feb-2001

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SLOVENSKI STANDARD
SIST ISO/TR 13387-6:2001
01-februar-2001

Požarno inženirstvo - 6. del: Odziv konstrukcije in širjenje požara izven prostora

nastanka požara

Fire safety engineering -- Part 6: Structural response and fire spread beyond the

enclosure of origin

Ingénierie de la sécurité contre l'incendie -- Partie 6: Réponse structurelle et propagation

du feu au delà de l'enceinte d'origine
Ta slovenski standard je istoveten z: ISO/TR 13387-6:1999
ICS:
13.220.01 Varstvo pred požarom na Protection against fire in
splošno general
SIST ISO/TR 13387-6:2001 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST ISO/TR 13387-6:2001
---------------------- Page: 2 ----------------------
SIST ISO/TR 13387-6:2001
TECHNICAL ISO/TR
REPORT 13387-6
First edition
1999-10-15
Fire safety engineering —
Part 6:
Structural response and fire spread beyond the
enclosure of origin
Ingénierie de la sécurité contre l'incendie —
Partie 6: Réponse structurelle et propagation du feu au-delà de l'enceinte
d'origine
Reference number
ISO/TR 13387-6:1999(E)
---------------------- Page: 3 ----------------------
SIST ISO/TR 13387-6:2001
ISO/TR 13387-6:1999(E)
Contents

1 Scope ........................................................................................................................................................................1

2 Normative references ..............................................................................................................................................1

3 Terms and definitions .............................................................................................................................................2

4 Symbols and abbreviated terms ............................................................................................................................3

5 Subsystem 3 of the total design system ...............................................................................................................3

6 Subsystem 3 evaluations........................................................................................................................................5

6.1 General...................................................................................................................................................................5

6.2 Thermal response.................................................................................................................................................5

6.3 Mechanical response............................................................................................................................................7

6.4 Fire spread.............................................................................................................................................................9

7 Engineering methods ............................................................................................................................................13

7.1 General.................................................................................................................................................................13

7.2 Estimation formulae ...........................................................................................................................................13

7.3 Computer models ...............................................................................................................................................13

7.4 Experimental methods .......................................................................................................................................14

8 Guidance for setting criteria.................................................................................................................................14

Bibliography..............................................................................................................................................................16

© 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 iso@iso.ch
Printed in Switzerland
---------------------- Page: 4 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(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 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 13387-6, 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
iii
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SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)
Introduction

An important feature of design for fire safety, whether it is undertaken employing prescriptive regulations or fire

safety engineering principles, is to ensure that building elements prevent (or delay) the spread of fire and prevent

(or delay) structural failure. Measures must be taken to ensure the spread of fire and structural failure do not

threaten the lives of occupants and firefighters, or compromise other fire safety objectives.

In prescriptive fire safety design, extensive use is made of the fire resistance of building elements as determined by

the standard fire resistance test ISO 834-1. Inherent in this test are criteria concerned with load-bearing capacity,

integrity and thermal insulation. Fire resistance requirements may be prescribed in national regulations and codes

according to the use of the building, the size of fire compartments and the height of the building.

Design may also be undertaken employing fire safety engineering principles in which neither the temperature-time

curve nor the duration of the exposing fire are prescribed. Instead, pertinent characteristics of the exposing fire are

calculated to be representative of one (or several) fire scenarios envisioned for the building. The thermal and

mechanical response of building elements subjected to such exposing fires are then calculated. Finally, the

performance of building elements (specifically their ability to inhibit fire spread and structural failure) are assessed

using criteria which, depending on the conditions at hand, may differ from the fire resistance criteria within

ISO 834-1.

This part of ISO/TR 13387 is intended for use together with the other Technical Reports as described in clause 5.

For some applications however this document alone may be sufficient.

Clause 6 describes and provides guidance on the approaches available to characterize the physical and chemical

processes which govern the thermal and mechanical responses of building elements exposed to fire.

Clause 7 is a discussion of engineering methods to predict the thermal and mechanical response of building

elements exposed to fire and thereby to evaluate the potential for fire spread and structural failure. It should be

noted that whatever method is selected, it should be assessed and verified using the principles documented in

ISO/TR 13387-3. Furthermore, special care should be taken when using input data published in the literature. The

quantitative information may be related to specific test conditions and/or specific commercial products, and the

application of the data under different conditions may result in significant errors.

Finally, in clause 8, guidance on interpreting the results of an analysis of the potential of structural failure and fire

spread is provided. This includes guidance on the selection of criteria for assessing the effectiveness of fire safety

measures meant to reduce the potential of structural failure or fire spread. The latter is only possible if the objectives

of fire safety design have been clearly specified.
---------------------- Page: 6 ----------------------
SIST ISO/TR 13387-6:2001
TECHNICAL REPORT © ISO ISO/TR 13387-6:1999(E)
Fire safety engineering —
Part 6:
Structural response and fire spread beyond the enclosure of origin
1 Scope

This part of ISO/TR 13387 is intended to provide general guidance on the use of engineering methods for the

prediction of fire spread within and between buildings, and for the prediction of the response of a structure exposed

to fire. The report is not intended as a detailed technical design guide, but could be used as the basis for

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 fire spread and for fire damage to a building's structure. It also provides guidance for

assessing the effectiveness of fire safety measures meant to reduce these potentials.

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 editions of the normative documents indicated below. For

undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC

maintain registers of currently valid International Standards.

ISO 834-1:1999, Fire-resistance tests — Elements of building construction — Part 1: General requirements.

ISO 7345:1987, Thermal insulation — Physical quantities and definitions.

ISO/TR 10158:1991, Principles and rationale underlying calculation methods in relation to fire resistance of

structural elements.

ISO/TR 12470:1998, Fire resistance tests — Guidance on the application and extension of results.

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/TR 13387-3, Fire safety engineering — Part 3: Assessment and verification of mathematical fire models.

ISO/TR 13387-4, Fire safety engineering — Part 4: Initiation and development of fire and generation of fire effluents.

ISO/TR 13387-5, Fire safety engineering — Part 5: Movement of fire effluents.
---------------------- Page: 7 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)

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 13943, Fire safety — Vocabulary.
3 Terms and definitions

For the purposes of this part of ISO/TR 13387, the definitions given in ISO 13943, ISO/TR 13387-1 and the

following apply.
3.1
building element

integral component of the structure or fabric of a building, including floors, walls, beams, columns, doors, etc.

complete with penetrations, but does not include building contents
3.2
enclosure
space defined by boundary elements
3.3
integrity

ability of a separating element, when exposed to fire on one side, to prevent the passage of flames and hot gases or

the occurrence of flames on the unexposed side
3.4
load-bearing capacity

ability of a building element (or structure) to sustain applied actions (loads) when exposed to fire

3.5
mechanical response

measure of fire induced changes to the deflection, stiffness and load-bearing capacity of building elements and the

development of openings (cracks) in building elements during fire exposure as a result of the shrinkage (expansion)

of materials, spalling, delamination, etc.
3.6
thermal diffusivity
2 -1

thermal conductivity divided by the density and specific heat, expressed in m ·s , given by k = k/(r·c)

3.7
thermal inertia

product of thermal conductivity, density and specific heat (square of thermal effusivity according to ISO 7345), given

by k·r·c,
2 -4 -2 -1
It is expressed in J ·m ·K ·s .
3.8
thermal insulation

the ability of a separating element, when exposed to fire on one side, to prevent the transmission of excessive heat

3.9
thermal response
a measure of:
a) fire induced changes to the temperature profile within building elements; and

b) the development of openings in building elements during fire exposure as a result of the melting of materials

---------------------- Page: 8 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)
4 Symbols and abbreviated terms
-1 -1
c specific heat of a material, expressed in J·kg ·K
-1 -1
k thermal conductivity, expressed in W·m ·K
2 -1
k thermal diffusivity, expressed in m ·s
r density, expressed in kg·m
5 Subsystem 3 of the total design system

The approach adopted in this part of ISO/TR 13387 is to acknowledge that assessment of structural response and

fire spread addresses only a subsection of the global objectives of fire safety design. Global design, described in

more detail in the framework document, ISO/TR 13387-1, is divided into subsystems. The key principles of the

global design approach are that interdependencies among the subsystems are evaluated and that pertinent

considerations for each subsystem are identified. Structural response and fire spread is subsystem 3 (SS3) of the

total fire safety design system.

In the framework document, global fire safety design is illustrated by an information bus analogy. The information

bus has three layers: global information, evaluations and process buses. The global information includes data which

are either transferred among subsystems or employed to make engineering decisions. SS3 links with the global

information are shown in Figure 1. The second layer of the bus system depicts the evaluations which must be

undertaken within SS3 to evaluate structural response and fire spread. The third layer elucidates the fundamental

processes which come into play in each evaluation undertaken within SS3.

SS3 draws on other subsystems for certain input data and generates output data which are used by yet other

subsystems. For example, SS1 provides predictions of the temperature and heat flux history (thermal profile) in the

enclosure of concern. These data along with the description of building assemblies (building parameters) are

employed by SS3 to predict the likelihood (and time) of fire spread, and the likelihood (and time) of structural failure.

Once a prediction has been made “output” data describing the building condition are placed on the global

information bus. Building condition data may subsequently become “input” data for evaluations undertaken by SS1

and SS2 to calculate, for example, the potential for fire spread (and the subsequent fire size).

The transfer of data between the global information bus and the evaluations undertaken in SS3 is depicted explicitly

in Figure 1. As Figure 1 indicates it is necessary to calculate (evaluate) the thermal response and mechanical

response of building systems and then determine whether fire spread will occur. Guidance on undertaking such

calculations is given in clause 6.

The fundamental processes which come into play in these evaluations are also depicted in Figure 1. An engineering

analysis will incorporate these fundamental processes to an appropriate level of rigour as discussed in clause 6.

It should be noted that Figure 1 has been constructed to elucidate the process involved in undertaking an evaluation

of the potential for structural failure or fire spread. It is not intended to include all possible phenomena.

---------------------- Page: 9 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)
ISO TC 92/SC 4 FIRE SAFETY ENGINEERING BUS SYSTEM

Subsystem 3 (SS3) — Structural response and fire spread beyond the enclosure of origin

Figure 1 — Illustration of the global information, evaluation and process buses for SS3

---------------------- Page: 10 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)
6 Subsystem 3 evaluations
6.1 General

In this clause, guidance on predicting and evaluating the thermal and mechanical response of building elements and

structures exposed to fire are discussed. Guidance on assessing whether fire spread will occur is also provided.

The input data required to undertaken such evaluations and the possible output information are identified. Where

possible, reference is made to literature which provides a more detailed discussion of the material presented in this

clause.
6.2 Thermal response
6.2.1 Role in fire safety engineering design

This clause provides an overview of the assessment of the thermal response of building elements which are in one

way or other exposed to heating from fire. The exposing fire may be a localized fire within an enclosure, a post-

flashover enclosure fire, or perhaps an external fire. The nature of the exposing fire will have already been derived

by SS1 or possibly specified as a design fire by ISO/TR 13387-2.

An accurate prediction of the thermal response of building elements exposed to fire is essential in fire safety

engineering design. In the first instance, it allows for an assessment of the degree of thermal damage that may be

sustained by building elements exposed to fire. This may be particularly important if a building is to be designed so

that it can be re-used following a fire. Of more immediate concern, prediction of the thermal response of building

elements is the first step in the assessment of their mechanical response and ultimately the potential for structural

failure and/or fire spread.

Detailed discussions of the mechanical response and potential for fire spread are provided in 6.3 and 6.4

respectively. However, it note that for some applications an assessment of the thermal response of building

elements coupled with well-defined performance criteria may suffice. This may be the case, for example, if a

structural member can be assumed to fail when it reaches a specific temperature as is often assumed for structural

steel elements. It may also be the case if it can be assumed that the spread of fire from one enclosure to another

may occur because of either the excessive transmission of heat through enclosure boundaries or because of

openings created by the melting of materials as both of these phenomena can also be tied to temperature rise

criteria. The question of establishing appropriate thermal criteria is briefly discussed in clause 8.

6.2.1.1 Input

As depicted in Figure 1, evaluation of the thermal response of building elements requires the following input data

from the global information bus:

 building parameters (dimensions, locations, thermophysical and thermochemical properties of building

elements);

 size of fire/smoke (for localized or external fires: physical size and relative location of fire to key building

elements);

 thermal (for all fires: the temperature-time profile of fire gases and the heat flux impinging on building

elements);

 pressure / velocity (the velocity of the fire gases may be needed to assess convective heat transfer from the

fire to building elements); and

 effluent species (smoke concentrations effect the emissivity of the fire gases. The emissivity may be needed to

assess radiative heat transfer from the fire to building elements).
---------------------- Page: 11 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)
6.2.1.2 Output

Once the evaluation of the thermal response of building elements is completed, the following data are passed to the

global information bus:

 building condition (temperature-time profile within and on the surface of building elements).

This output also becomes input for assessing the mechanical response of building elements and the potential for

fire spread.
6.2.2 Modelling the thermal response of building elements

As indicated in 6.2.1.1, to model the thermal response of building elements, a reasonably detailed description of the

exposing fire is necessary. This document is intended to be used as part of a fire safety engineering assessment in

which SS1 has first calculated the pertinent properties of the exposing fire (whether it be an enclosure fire, a

localized fire or an external fire). There are, however, applications for which the exposing fire can be chosen from a

set of design fires. Care must be exercised when selecting an appropriate design fire as some constructions may be

sensitive to high temperatures whereas others may be sensitive to high rates of temperature rise or to the duration

of exposure. Further guidance on the use of design fires is found in ISO/TR 13387-2.

Once the exposing fire has been chosen an assessment of the thermal response of building elements can begin

(see Figure 1). The calculation of heat transfer to and within the building elements undertaken by SS3 will need to

be more detailed than the calculation already undertaken by SS1 where it was the temperature of the fire gases that

was of primary interest.

If a building element is in direct contact with fire gases (for example, in a post-flashover enclosure fire), heat is

transferred to exposed surfaces of the element by means of radiation (see reference [1] in the bibliography) and

convection (see reference [2]). On the other hand, if a building element is some distance from flames or hot gases

(for example, for exposure to fire in a neighbouring building), “exposed” surfaces may be heated by radiation but

cooled by convection. Engineering methods for modelling radiative and convective heat transfer for fire safety

engineering calculations are readily available (see references [1] and [2]).

In either case, heat is transferred from the hot surface deeper into the element by means of heat conduction (see

reference [3]). As heat is conducted into the element, any absorbed water is vaporized (a phase change) and the

element itself may experience melting (a phase change) or thermal degradation. These processes are commonly

endothermic and hence slow down heat transmission. The vapours generated by vaporization of water and by

thermal degradation of the element will migrate through the element further impacting on the heat transfer process.

In principle, then, heat transfer and mass transfer (gas flow) are coupled. The equations governing these processes

are complex and can only be solved by the use of numerical methods.

For some materials, the internal processes discussed above are not present or do not unduly impact upon heat flow

so that heat transfer through the material can be assumed to obey the 3-dimensional heat conduction (see

reference [3]). Nonetheless, the material's thermal conductivity (k), specific heat (c) and perhaps even density (r)

are commonly temperature dependent. Despite these simplifications, the heat conduction equation with temperature

dependent coefficients can also only be solved by the use of numerical methods.

Analysis can be further simplified if the material's thermal properties (k, c and r) can be assumed to be constant (or

at least can be replaced by an average value) over the temperature range of interest. Due to the complex nature of

radiative heating at the surface (boundary conditions) the heat conduction equation can still only be solved explicitly

by the use of numerical methods. Nonetheless, the structure of the equation reveals interesting dependencies on

the thermal properties. For example, in the early stages of the heating, the increase of the temperature of a surface

1/2

exposed to radiative and/or convective heating as a function of time is proportional to (k·r·c) ; that is, to the

inverse of the square root of the thermal inertia. On the other hand, the time-dependent temperature profile within

the material can be shown to depend upon the material's thermal diffusivity k.

For materials which have very large thermal conductivity or which are very thin, it is sometimes possible to

completely ignore heat conduction. In such cases, a lumped heat capacity model can be constructed whereby the

entire element is assumed to be at a uniform temperature. Nonetheless, the element is still heated at the surface by

radiation and convection.
---------------------- Page: 12 ----------------------
SIST ISO/TR 13387-6:2001
© ISO
ISO/TR 13387-6:1999(E)

Further discussion of engineering methods for modelling the thermal response of building elements exposed to fire

is provided in clause 7 of this part of ISO/TR 13387 and in ISO/TR 10158.
6.3 Mechanical response
6.3.1 Role in fire safety engineering design

This subclause provides an overview of the assessment of the mechanical response of building elements and the

building structure when exposed to heating from fire. This analysis is undertaken using as input data the time-

dependent temperature profiles within elements which have been calculated following the procedures outlined in

6.2.

The term mechanical response is used to denote two important facets of a building element's response to fire.

Firstly, it is a measure of fire induced changes to the deflection, stiffness and load-bearing capacity of the element.

Secondly, it is a measure of the development of openings (cracks) in the element as a result of the shrinkage

(expansion) of materials, spalling, delamination, etc.

An accurate prediction of the mechanical response of building elements exposed to fire is essential in fire safety

engineering design. In the first instance, it allows for an assessment of the degree of mechanical damage that may

be sustained by building elements exposed to fire. This may be particularly important if a building is to be designed

so that it can be re-used following a fire. Of more immediate concern, prediction of the mechanical response of

building elements is necessary step in the assessment of the potential for structural failure and/or fire spread.

Detailed discussions of the potential for fire spread are provided in 6.4. However, it should be noted that for some

applications an assessment of the thermal and, then, mechanical response of building elements coupled with well-

defined performance criteria may suffice. This may be the case, for example, if a structural member can be shown

to undergo excessive deflection. It may also be the case if it can be assumed that the spread of fire from one

enclosure to another may occur because of openings created by the shrinkage (expansion) of materials, spalling,

delamination, etc. The question of establishing appropriate criteria is briefly discussed in clause 8.

6.3.1.1 Input

As depicted in Figure 1, evaluation of the mechanical response of building elements requires the following input

data from the global information bus:

 building parameters (mechanical properties of building elements, structural loads supported by building

elements);

 building condition (temperature-time profile within and on the surface of building elements); and

 pressure and/or velocity (pressure distributions may have an impact on integrity and structural performance).

6.3.1.2 Output

Once the evaluation of the mechanical response of building elements is completed, the following data are passed to

the global information bus:
 building condition (integrity of building eleme
...

TECHNICAL ISO/TR
REPORT 13387-6
First edition
1999-10-15
Fire safety engineering —
Part 6:
Structural response and fire spread beyond the
enclosure of origin
Ingénierie de la sécurité contre l'incendie —
Partie 6: Réponse structurelle et propagation du feu au-delà de l'enceinte
d'origine
Reference number
ISO/TR 13387-6:1999(E)
---------------------- Page: 1 ----------------------
ISO/TR 13387-6:1999(E)
Contents

1 Scope ........................................................................................................................................................................1

2 Normative references ..............................................................................................................................................1

3 Terms and definitions .............................................................................................................................................2

4 Symbols and abbreviated terms ............................................................................................................................3

5 Subsystem 3 of the total design system ...............................................................................................................3

6 Subsystem 3 evaluations........................................................................................................................................5

6.1 General...................................................................................................................................................................5

6.2 Thermal response.................................................................................................................................................5

6.3 Mechanical response............................................................................................................................................7

6.4 Fire spread.............................................................................................................................................................9

7 Engineering methods ............................................................................................................................................13

7.1 General.................................................................................................................................................................13

7.2 Estimation formulae ...........................................................................................................................................13

7.3 Computer models ...............................................................................................................................................13

7.4 Experimental methods .......................................................................................................................................14

8 Guidance for setting criteria.................................................................................................................................14

Bibliography..............................................................................................................................................................16

© 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 iso@iso.ch
Printed in Switzerland
---------------------- Page: 2 ----------------------
© ISO
ISO/TR 13387-6:1999(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 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 13387-6, 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
iii
---------------------- Page: 3 ----------------------
© ISO
ISO/TR 13387-6:1999(E)
Introduction

An important feature of design for fire safety, whether it is undertaken employing prescriptive regulations or fire

safety engineering principles, is to ensure that building elements prevent (or delay) the spread of fire and prevent

(or delay) structural failure. Measures must be taken to ensure the spread of fire and structural failure do not

threaten the lives of occupants and firefighters, or compromise other fire safety objectives.

In prescriptive fire safety design, extensive use is made of the fire resistance of building elements as determined by

the standard fire resistance test ISO 834-1. Inherent in this test are criteria concerned with load-bearing capacity,

integrity and thermal insulation. Fire resistance requirements may be prescribed in national regulations and codes

according to the use of the building, the size of fire compartments and the height of the building.

Design may also be undertaken employing fire safety engineering principles in which neither the temperature-time

curve nor the duration of the exposing fire are prescribed. Instead, pertinent characteristics of the exposing fire are

calculated to be representative of one (or several) fire scenarios envisioned for the building. The thermal and

mechanical response of building elements subjected to such exposing fires are then calculated. Finally, the

performance of building elements (specifically their ability to inhibit fire spread and structural failure) are assessed

using criteria which, depending on the conditions at hand, may differ from the fire resistance criteria within

ISO 834-1.

This part of ISO/TR 13387 is intended for use together with the other Technical Reports as described in clause 5.

For some applications however this document alone may be sufficient.

Clause 6 describes and provides guidance on the approaches available to characterize the physical and chemical

processes which govern the thermal and mechanical responses of building elements exposed to fire.

Clause 7 is a discussion of engineering methods to predict the thermal and mechanical response of building

elements exposed to fire and thereby to evaluate the potential for fire spread and structural failure. It should be

noted that whatever method is selected, it should be assessed and verified using the principles documented in

ISO/TR 13387-3. Furthermore, special care should be taken when using input data published in the literature. The

quantitative information may be related to specific test conditions and/or specific commercial products, and the

application of the data under different conditions may result in significant errors.

Finally, in clause 8, guidance on interpreting the results of an analysis of the potential of structural failure and fire

spread is provided. This includes guidance on the selection of criteria for assessing the effectiveness of fire safety

measures meant to reduce the potential of structural failure or fire spread. The latter is only possible if the objectives

of fire safety design have been clearly specified.
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TECHNICAL REPORT © ISO ISO/TR 13387-6:1999(E)
Fire safety engineering —
Part 6:
Structural response and fire spread beyond the enclosure of origin
1 Scope

This part of ISO/TR 13387 is intended to provide general guidance on the use of engineering methods for the

prediction of fire spread within and between buildings, and for the prediction of the response of a structure exposed

to fire. The report is not intended as a detailed technical design guide, but could be used as the basis for

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 fire spread and for fire damage to a building's structure. It also provides guidance for

assessing the effectiveness of fire safety measures meant to reduce these potentials.

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 editions of the normative documents indicated below. For

undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC

maintain registers of currently valid International Standards.

ISO 834-1:1999, Fire-resistance tests — Elements of building construction — Part 1: General requirements.

ISO 7345:1987, Thermal insulation — Physical quantities and definitions.

ISO/TR 10158:1991, Principles and rationale underlying calculation methods in relation to fire resistance of

structural elements.

ISO/TR 12470:1998, Fire resistance tests — Guidance on the application and extension of results.

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/TR 13387-3, Fire safety engineering — Part 3: Assessment and verification of mathematical fire models.

ISO/TR 13387-4, Fire safety engineering — Part 4: Initiation and development of fire and generation of fire effluents.

ISO/TR 13387-5, Fire safety engineering — Part 5: Movement of fire effluents.
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© ISO
ISO/TR 13387-6:1999(E)

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 13943, Fire safety — Vocabulary.
3 Terms and definitions

For the purposes of this part of ISO/TR 13387, the definitions given in ISO 13943, ISO/TR 13387-1 and the

following apply.
3.1
building element

integral component of the structure or fabric of a building, including floors, walls, beams, columns, doors, etc.

complete with penetrations, but does not include building contents
3.2
enclosure
space defined by boundary elements
3.3
integrity

ability of a separating element, when exposed to fire on one side, to prevent the passage of flames and hot gases or

the occurrence of flames on the unexposed side
3.4
load-bearing capacity

ability of a building element (or structure) to sustain applied actions (loads) when exposed to fire

3.5
mechanical response

measure of fire induced changes to the deflection, stiffness and load-bearing capacity of building elements and the

development of openings (cracks) in building elements during fire exposure as a result of the shrinkage (expansion)

of materials, spalling, delamination, etc.
3.6
thermal diffusivity
2 -1

thermal conductivity divided by the density and specific heat, expressed in m ·s , given by k = k/(r·c)

3.7
thermal inertia

product of thermal conductivity, density and specific heat (square of thermal effusivity according to ISO 7345), given

by k·r·c,
2 -4 -2 -1
It is expressed in J ·m ·K ·s .
3.8
thermal insulation

the ability of a separating element, when exposed to fire on one side, to prevent the transmission of excessive heat

3.9
thermal response
a measure of:
a) fire induced changes to the temperature profile within building elements; and

b) the development of openings in building elements during fire exposure as a result of the melting of materials

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© ISO
ISO/TR 13387-6:1999(E)
4 Symbols and abbreviated terms
-1 -1
c specific heat of a material, expressed in J·kg ·K
-1 -1
k thermal conductivity, expressed in W·m ·K
2 -1
k thermal diffusivity, expressed in m ·s
r density, expressed in kg·m
5 Subsystem 3 of the total design system

The approach adopted in this part of ISO/TR 13387 is to acknowledge that assessment of structural response and

fire spread addresses only a subsection of the global objectives of fire safety design. Global design, described in

more detail in the framework document, ISO/TR 13387-1, is divided into subsystems. The key principles of the

global design approach are that interdependencies among the subsystems are evaluated and that pertinent

considerations for each subsystem are identified. Structural response and fire spread is subsystem 3 (SS3) of the

total fire safety design system.

In the framework document, global fire safety design is illustrated by an information bus analogy. The information

bus has three layers: global information, evaluations and process buses. The global information includes data which

are either transferred among subsystems or employed to make engineering decisions. SS3 links with the global

information are shown in Figure 1. The second layer of the bus system depicts the evaluations which must be

undertaken within SS3 to evaluate structural response and fire spread. The third layer elucidates the fundamental

processes which come into play in each evaluation undertaken within SS3.

SS3 draws on other subsystems for certain input data and generates output data which are used by yet other

subsystems. For example, SS1 provides predictions of the temperature and heat flux history (thermal profile) in the

enclosure of concern. These data along with the description of building assemblies (building parameters) are

employed by SS3 to predict the likelihood (and time) of fire spread, and the likelihood (and time) of structural failure.

Once a prediction has been made “output” data describing the building condition are placed on the global

information bus. Building condition data may subsequently become “input” data for evaluations undertaken by SS1

and SS2 to calculate, for example, the potential for fire spread (and the subsequent fire size).

The transfer of data between the global information bus and the evaluations undertaken in SS3 is depicted explicitly

in Figure 1. As Figure 1 indicates it is necessary to calculate (evaluate) the thermal response and mechanical

response of building systems and then determine whether fire spread will occur. Guidance on undertaking such

calculations is given in clause 6.

The fundamental processes which come into play in these evaluations are also depicted in Figure 1. An engineering

analysis will incorporate these fundamental processes to an appropriate level of rigour as discussed in clause 6.

It should be noted that Figure 1 has been constructed to elucidate the process involved in undertaking an evaluation

of the potential for structural failure or fire spread. It is not intended to include all possible phenomena.

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© ISO
ISO/TR 13387-6:1999(E)
ISO TC 92/SC 4 FIRE SAFETY ENGINEERING BUS SYSTEM

Subsystem 3 (SS3) — Structural response and fire spread beyond the enclosure of origin

Figure 1 — Illustration of the global information, evaluation and process buses for SS3

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© ISO
ISO/TR 13387-6:1999(E)
6 Subsystem 3 evaluations
6.1 General

In this clause, guidance on predicting and evaluating the thermal and mechanical response of building elements and

structures exposed to fire are discussed. Guidance on assessing whether fire spread will occur is also provided.

The input data required to undertaken such evaluations and the possible output information are identified. Where

possible, reference is made to literature which provides a more detailed discussion of the material presented in this

clause.
6.2 Thermal response
6.2.1 Role in fire safety engineering design

This clause provides an overview of the assessment of the thermal response of building elements which are in one

way or other exposed to heating from fire. The exposing fire may be a localized fire within an enclosure, a post-

flashover enclosure fire, or perhaps an external fire. The nature of the exposing fire will have already been derived

by SS1 or possibly specified as a design fire by ISO/TR 13387-2.

An accurate prediction of the thermal response of building elements exposed to fire is essential in fire safety

engineering design. In the first instance, it allows for an assessment of the degree of thermal damage that may be

sustained by building elements exposed to fire. This may be particularly important if a building is to be designed so

that it can be re-used following a fire. Of more immediate concern, prediction of the thermal response of building

elements is the first step in the assessment of their mechanical response and ultimately the potential for structural

failure and/or fire spread.

Detailed discussions of the mechanical response and potential for fire spread are provided in 6.3 and 6.4

respectively. However, it note that for some applications an assessment of the thermal response of building

elements coupled with well-defined performance criteria may suffice. This may be the case, for example, if a

structural member can be assumed to fail when it reaches a specific temperature as is often assumed for structural

steel elements. It may also be the case if it can be assumed that the spread of fire from one enclosure to another

may occur because of either the excessive transmission of heat through enclosure boundaries or because of

openings created by the melting of materials as both of these phenomena can also be tied to temperature rise

criteria. The question of establishing appropriate thermal criteria is briefly discussed in clause 8.

6.2.1.1 Input

As depicted in Figure 1, evaluation of the thermal response of building elements requires the following input data

from the global information bus:

 building parameters (dimensions, locations, thermophysical and thermochemical properties of building

elements);

 size of fire/smoke (for localized or external fires: physical size and relative location of fire to key building

elements);

 thermal (for all fires: the temperature-time profile of fire gases and the heat flux impinging on building

elements);

 pressure / velocity (the velocity of the fire gases may be needed to assess convective heat transfer from the

fire to building elements); and

 effluent species (smoke concentrations effect the emissivity of the fire gases. The emissivity may be needed to

assess radiative heat transfer from the fire to building elements).
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© ISO
ISO/TR 13387-6:1999(E)
6.2.1.2 Output

Once the evaluation of the thermal response of building elements is completed, the following data are passed to the

global information bus:

 building condition (temperature-time profile within and on the surface of building elements).

This output also becomes input for assessing the mechanical response of building elements and the potential for

fire spread.
6.2.2 Modelling the thermal response of building elements

As indicated in 6.2.1.1, to model the thermal response of building elements, a reasonably detailed description of the

exposing fire is necessary. This document is intended to be used as part of a fire safety engineering assessment in

which SS1 has first calculated the pertinent properties of the exposing fire (whether it be an enclosure fire, a

localized fire or an external fire). There are, however, applications for which the exposing fire can be chosen from a

set of design fires. Care must be exercised when selecting an appropriate design fire as some constructions may be

sensitive to high temperatures whereas others may be sensitive to high rates of temperature rise or to the duration

of exposure. Further guidance on the use of design fires is found in ISO/TR 13387-2.

Once the exposing fire has been chosen an assessment of the thermal response of building elements can begin

(see Figure 1). The calculation of heat transfer to and within the building elements undertaken by SS3 will need to

be more detailed than the calculation already undertaken by SS1 where it was the temperature of the fire gases that

was of primary interest.

If a building element is in direct contact with fire gases (for example, in a post-flashover enclosure fire), heat is

transferred to exposed surfaces of the element by means of radiation (see reference [1] in the bibliography) and

convection (see reference [2]). On the other hand, if a building element is some distance from flames or hot gases

(for example, for exposure to fire in a neighbouring building), “exposed” surfaces may be heated by radiation but

cooled by convection. Engineering methods for modelling radiative and convective heat transfer for fire safety

engineering calculations are readily available (see references [1] and [2]).

In either case, heat is transferred from the hot surface deeper into the element by means of heat conduction (see

reference [3]). As heat is conducted into the element, any absorbed water is vaporized (a phase change) and the

element itself may experience melting (a phase change) or thermal degradation. These processes are commonly

endothermic and hence slow down heat transmission. The vapours generated by vaporization of water and by

thermal degradation of the element will migrate through the element further impacting on the heat transfer process.

In principle, then, heat transfer and mass transfer (gas flow) are coupled. The equations governing these processes

are complex and can only be solved by the use of numerical methods.

For some materials, the internal processes discussed above are not present or do not unduly impact upon heat flow

so that heat transfer through the material can be assumed to obey the 3-dimensional heat conduction (see

reference [3]). Nonetheless, the material's thermal conductivity (k), specific heat (c) and perhaps even density (r)

are commonly temperature dependent. Despite these simplifications, the heat conduction equation with temperature

dependent coefficients can also only be solved by the use of numerical methods.

Analysis can be further simplified if the material's thermal properties (k, c and r) can be assumed to be constant (or

at least can be replaced by an average value) over the temperature range of interest. Due to the complex nature of

radiative heating at the surface (boundary conditions) the heat conduction equation can still only be solved explicitly

by the use of numerical methods. Nonetheless, the structure of the equation reveals interesting dependencies on

the thermal properties. For example, in the early stages of the heating, the increase of the temperature of a surface

1/2

exposed to radiative and/or convective heating as a function of time is proportional to (k·r·c) ; that is, to the

inverse of the square root of the thermal inertia. On the other hand, the time-dependent temperature profile within

the material can be shown to depend upon the material's thermal diffusivity k.

For materials which have very large thermal conductivity or which are very thin, it is sometimes possible to

completely ignore heat conduction. In such cases, a lumped heat capacity model can be constructed whereby the

entire element is assumed to be at a uniform temperature. Nonetheless, the element is still heated at the surface by

radiation and convection.
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© ISO
ISO/TR 13387-6:1999(E)

Further discussion of engineering methods for modelling the thermal response of building elements exposed to fire

is provided in clause 7 of this part of ISO/TR 13387 and in ISO/TR 10158.
6.3 Mechanical response
6.3.1 Role in fire safety engineering design

This subclause provides an overview of the assessment of the mechanical response of building elements and the

building structure when exposed to heating from fire. This analysis is undertaken using as input data the time-

dependent temperature profiles within elements which have been calculated following the procedures outlined in

6.2.

The term mechanical response is used to denote two important facets of a building element's response to fire.

Firstly, it is a measure of fire induced changes to the deflection, stiffness and load-bearing capacity of the element.

Secondly, it is a measure of the development of openings (cracks) in the element as a result of the shrinkage

(expansion) of materials, spalling, delamination, etc.

An accurate prediction of the mechanical response of building elements exposed to fire is essential in fire safety

engineering design. In the first instance, it allows for an assessment of the degree of mechanical damage that may

be sustained by building elements exposed to fire. This may be particularly important if a building is to be designed

so that it can be re-used following a fire. Of more immediate concern, prediction of the mechanical response of

building elements is necessary step in the assessment of the potential for structural failure and/or fire spread.

Detailed discussions of the potential for fire spread are provided in 6.4. However, it should be noted that for some

applications an assessment of the thermal and, then, mechanical response of building elements coupled with well-

defined performance criteria may suffice. This may be the case, for example, if a structural member can be shown

to undergo excessive deflection. It may also be the case if it can be assumed that the spread of fire from one

enclosure to another may occur because of openings created by the shrinkage (expansion) of materials, spalling,

delamination, etc. The question of establishing appropriate criteria is briefly discussed in clause 8.

6.3.1.1 Input

As depicted in Figure 1, evaluation of the mechanical response of building elements requires the following input

data from the global information bus:

 building parameters (mechanical properties of building elements, structural loads supported by building

elements);

 building condition (temperature-time profile within and on the surface of building elements); and

 pressure and/or velocity (pressure distributions may have an impact on integrity and structural performance).

6.3.1.2 Output

Once the evaluation of the mechanical response of building elements is completed, the following data are passed to

the global information bus:

 building condition (integrity of building elements and load-bearing capacity of building elements).

This output also becomes input for assessing the potential for structural collapse and fire spread.

6.3.2 Modelling the mechanical response of building elements

As indicated in 6.3.1.1, to model the mechanical response of individual building elements or of the building structure,

the time-dependent temperature profiles within the elements are necessary. Although it is likely that in a fire safety

engineering analysis these profiles will have been calculated following the procedures outlined in 6.2, such profiles

are also available in graphical form for some elements exposed to the standard temperature-time curve defined in

ISO 834-1 and for certain simulated natural fires.
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© ISO
ISO/TR 13387-6:1999(E)

The mechanical properties of a building element, such as its modulus of elasticity or its yield stress, can be both

temperature and thermal history dependent. Assessment of the structural response (in particular, assessment of

thermal expansion, deflections or load bearing capacity) is oft
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