Fire safety engineering -- Part 2: Design fire scenarios and design fires

Ingénierie de la sécurité contre l'incendie -- Partie 2: Conception des scénarios-incendie et des feux

Požarno inženirstvo - 2. del: Požarni scenariji

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 13387-2:2001
01-februar-2001
Požarno inženirstvo - 2. del: Požarni scenariji
Fire safety engineering -- Part 2: Design fire scenarios and design fires

Ingénierie de la sécurité contre l'incendie -- Partie 2: Conception des scénarios-incendie

et des feux
Ta slovenski standard je istoveten z: ISO/TR 13387-2:1999
ICS:
13.220.01 Varstvo pred požarom na Protection against fire in
splošno general
SIST ISO/TR 13387-2:2001 en

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

---------------------- Page: 1 ----------------------
SIST ISO/TR 13387-2:2001
---------------------- Page: 2 ----------------------
SIST ISO/TR 13387-2:2001
TECHNICAL ISO/TR
REPORT 13387-2
First edition
1999-10-15
Fire safety engineering —
Part 2:
Design fire scenarios and design fires
Ingénierie de la sécurité contre l'incendie —
Partie 2: Conception des scénarios-incendie et des feux
Reference number
ISO/TR 13387-2:1999(E)
---------------------- Page: 3 ----------------------
SIST ISO/TR 13387-2:2001
ISO/TR 13387-2:1999(E)
Contents

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

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

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

4 Symbols and abbreviated terms ............................................................................................................................2

5 Design fire scenarios...............................................................................................................................................3

5.1 Role of design fire scenarios in fire safety design............................................................................................3

5.2 Identification of important design fire scenarios ..............................................................................................4

6 Design fires ..............................................................................................................................................................8

6.1 Role of design fires in fire safety engineering...................................................................................................8

6.2 Characteristics of design fires ............................................................................................................................8

6.3 Characteristic fire growth ..................................................................................................................................10

6.4 Events modifying the design fire ......................................................................................................................10

6.5 Pre-flashover design fires..................................................................................................................................11

6.6 Fully developed fires ..........................................................................................................................................13

6.7 External design fires...........................................................................................................................................15

Annex A (informative) Typical fire growth categories ...........................................................................................16

Bibliography..............................................................................................................................................................17

© 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 13387-2:2001
© ISO
ISO/TR 13387-2:1999(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 13387-2, 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
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
Introduction

The specification of appropriate design fire scenarios and design fires are a crucial aspect of fire safety design. The

assumptions made with regard to these factors have a major impact on all aspects of the design as they represent

the input into most of the quantification processes.

A design fire scenario is the description of the course of a particular fire with respect to time and space. It includes

the impact on the fire of building features, occupants, fire safety systems and all other factors. It would typically

define the ignition source and process, the growth of fire on the first item ignited, the spread of fire, the interaction of

the fire with its environment and its decay and extinction. It also includes the interaction of this fire with the building

occupants and the interaction with the features and fire safety systems within the building.

ISO/TR 13387-1 provides a framework for the quantitative fire safety engineering assessment of buildings using

time-dependent calculations. Fire scenario analysis forms the basis of the method described.

The basis of these calculations is the design fire. A design fire is an idealisation of real fires that may occur in the

building. Design fires are described in terms of the variation with time of variables used in the quantitative analysis.

These variables typically include heat release rate, fire size, yield of toxic species and yield of soot.

Where the calculation methods used are not able to predict fire growth and spread to other objects within the

compartment of origin or beyond, such growth and spread needs to be specified by the analyst as part of the design

fire, satisfying the functions of both SS2 and SS3.
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SIST ISO/TR 13387-2:2001
TECHNICAL REPORT © ISO ISO/TR 13387-2:1999(E)
Fire safety engineering —
Part 2:
Design fire scenarios and design fires
1 Scope

This part of ISO/TR 13387 provides guidance on the identification of appropriate design fire scenarios for

consideration in fire safety design. It also provides guidance on the specification of design fires for quantitative

analysis in fire safety design of buildings. This approach may be applied to other constructions. It is intended for use

in conjunction with the methodology outlined in part 1 of this Technical Report.

The document describes a systematic approach to the identification of significant fire scenarios that need to be

considered in fire safety design. Once significant fire scenarios have been identified, the document provides

guidance on the selection of "design fire scenarios“ for quantitative analysis.

The document provides guidance on the specification of "design fires“ to reflect the design fire scenarios that have

been identified for analysis. Design fires are specified in terms of important characteristics that form the input data

into the quantitative analysis of various subsystems of the fire safety system as described in part 1.

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/TR 13387-1, Fire safety engineering — Part 1: Application of fire performance concepts to design objectives.

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.

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 13943, Fire safety — Vocabulary.
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
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
design fire

a quantitative description of assumed fire characteristics within the design fire scenario

Typically, it is an idealised description of the variation with time of important fire variables such as heat release rate,

fire propagation, smoke and toxic species yield and temperature.
3.2
design fire scenario
a specific fire scenario on which an analysis will be conducted
3.3
engineering judgement

the process exercised by a professional who is qualified by way of education, experience and recognised skills to

complement, supplement, accept or reject elements of a quantitative analysis
3.4
fire scenario

a qualitative description of the course of a fire with time, identifying key events that characterise the fire and

differentiate it from other possible fires

It typically defines the ignition and fire growth process, the fully developed stage and the decay stage, together with

the building environment and systems that will impact on the course of the fire.
3.5
relative risk
the relative potential for realisation of an unwanted event

It is the product of the probability of occurrence of a consequence and the magnitude of the consequence based on

numbers that are only internally consistent within the set being compared and does not represent the actual risk in

absolute values.
4 Symbols and abbreviated terms
A Area of window opening, expressed in m
g Acceleration due to gravity, expressed in m/s
h Height of window, expressed in m
Q Heat release rate, expressed in MW
m Rate of inflow of air, expressed in kg/s
air
m Rate of volatilisation of fuel, expressed in kg/s
R Burning rate (wood equivalent) , expressed in kg/s
r Stoichiometric air/fuel ratio
rDensity, expressed in kg/m
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
t Time, expressed in s, min or h
T Ambient temperature, expressed in °C
T Fire gas temperature, expressed in °C
T Temperature of fire at window, expressed in °C
T Flame temperature along the vertical axis, expressed in °C
w Aggregate window width of enclosure, expressed in m
X Flame length along axis of flame, expressed in m
z Vertical distance, expressed in m
z Flame height, expressed in m
5 Design fire scenarios
5.1 Role of design fire scenarios in fire safety design

Design fire scenarios are at the core of the fire safety engineering methodology described in all parts of

ISO/TR 13387. The methodology is based on 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 set. Identification of the appropriate scenarios requiring analysis is crucial to the attainment of a building

that fulfils the fire safety performance objectives.

In reality, the number of possible fire scenarios in most buildings approaches infinity. It would be impossible to

analyse all scenarios even with the aid of the most sophisticated computing resources. This infinite set of

possibilities needs to be reduced to a finite set of design fire scenarios that are amenable to analysis and the results

of which represent an acceptable upper limit to the fire risk. That is to say that more onerous fire scenarios have an

acceptable probability of occurring and that the consequences of those scenarios would need to be borne by

society. The outcome of these extreme scenarios may be mitigated by additional factors that are often outside the

scope of the analysis. Regulatory authority input into, and concurrence with, the selection of the design fire

scenarios is most desirable.

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

each of the fire safety subsystems, different internal ventilation conditions and different external environmental

conditions. The possible consequences of each design fire scenario need to be considered.

Important design fire scenarios need to be identified during the qualitative design review (QDR) stage. During this

process, it is possible to eliminate scenarios that are of low consequence or have a very low probability of

occurrence from further consideration (see 5.2.4). It is important to remember that smouldering fires may have the

potential to cause a large number of fatalities in certain occupancies such as residential buildings.

Each design fire scenario is represented by a unique occurrence of events and is the result of a particular set of

circumstances associated with the fire safety measures. Accordingly, a design fire scenario represents a particular

combination of outcomes or events associated with factors such as:
 type of fire;
 internal ventilation conditions;
 external environmental conditions;
 performance of each of the fire safety measures;
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
 type, size and location of ignition source;
 distribution and type of fuel;
 fire load density;
fire suppression;
 state of doors;
 breakage of windows;
 building air-handling system.

Design fires may be needed for a wide range of design fire scenarios. These may be internal or external fire

scenarios. Examples of typical design fire scenarios include:
a) Internal
 room fire (corner, ceiling, floor, wall);
 fire in stairwells;
 single burning item fire (furniture, wastepaper basket, fittings);
 developing fire (smoke extraction);
 cable tray or duct fire;
 roof fires (under roof);
 cavity fire (wall cavity, facade, plenum).
b) External
 fire in neighbouring building;
 fires in external fuel packages;
 fires on roofs;
 fires on facades.

Other design fire scenarios may be agreed upon during the QDR for special situations.

5.2 Identification of important design fire scenarios
5.2.1 General

A systematic approach to the identification of fire scenarios for analysis is desirable in order to identify all important

scenarios and to provide a consistent approach by different analysts.

Generally, several design fire scenarios must be applied to the building under consideration to meet different

requirements. At least one fire scenario should be considered for structural hazards and one for life safety hazards.

A risk-ranking process is recommended as the most appropriate basis for the selection of design fire scenarios.

Such a process takes into account both the consequences and likelihood of the scenario.

Key aspects of the risk-ranking process, explained in the detailed steps below, are:

 identification of a comprehensive set of possible fire scenarios;
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)

 estimation of the probability of occurrence of the scenario using available data and engineering judgement;

 estimation of the consequence of the scenario using engineering judgement;

 estimation of the relative risk of the scenarios (product of consequence and probability of occurrence);

ranking of the fire scenarios according to the relative risk.

Design fire scenarios may need to consider not only the impact of all of the fire safety provisions on the chosen

design fire but also the partial or complete failure of fire safety provisions.

Generally, fire scenarios involving simultaneous failure of a number of reliable fire safety systems properly

maintained need not be considered as the combined probability of such scenarios are very low. However, if they are

associated with very severe consequences, where the resultant risk is significant, then they need to be considered.

Fire incident statistics provide an appropriate basis for identification of the initial set of possible design fire

scenarios. Fire statistics can be used to identify both the most common types of fire as well as the most hazardous

type of fire for a particular occupancy.

The following systematic approach towards identifying possible design fire scenarios is recommended. It is

recognised that alternative means of identifying design fire scenarios may be used.

5.2.2 Step 1 — Type of fire

From fire incident statistics appropriate for the building and occupancy under consideration, identify:

a) the most likely type of fire scenario;
b) the most likely severe-consequence fire scenario.

The most likely type of fire scenario can be determined from consideration of the items most commonly ignited, the

ignition source and location of the fire from relevant fire incident statistics.

The most likely severe-consequence fire scenario can be determined by consideration of a subset of the fire

incident statistics based upon an appropriate measure of the consequences, such as life loss or property loss. From

this subset of severe-consequence incidents, appropriate for the building and occupancy under consideration, the

most likely severe-consequence fire scenario can be identified.

If appropriate national statistics are not available, then information from other countries with similar fire experience

may be utilised. Care needs to be exercised in applying fire incident statistics to ensure that the data is appropriate

for the building under consideration.
5.2.3 Step 2 — Location of fire

For each of the scenarios identified in step 1, select a specific location or locations in the building that would

produce the most adverse fire scenario(s).
5.2.4 Step 3 — Potential fire hazards

Consider the fire scenarios that could arise from the potential fire hazards identified during the qualitative design

review phase.

Identify other critical severe-consequence scenarios for consideration. These scenarios typically involve:

 fires in assembly areas;
 fires within the egress system;
 fires blocking entry into the egress system;
 fires leading to structural collapse;
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
 fires involving high-hazard materials;
 fires exhibiting rapid growth.

If any of these scenarios is likely to have more severe consequences than those identified previously, they need to

be included in the set for analysis. They may replace less hazardous scenarios that are similar in nature.

5.2.5 Step 4 — Systems impacting on fire

Identify the building and fire safety system features which are likely to have a significant impact on the course of the

fire or the development of untenable conditions. Typical factors for consideration and their states include:

 type of fire (smouldering or flaming);
 wind (calm or representative of the location);
 doors and other openings in the enclosure of fire origin (open or closed);
 active suppression system (successful or unsuccessful in controlling fire);
 smoke management system (performed as expected or reduced performance);
 windows (glass intact or glass breaks);
 fire detection system (functions as designed or reduced performance);
 materials control (effective in limiting fire growth or not);

 warning and communication system (functions as designed or reduced performance);

 compartmentation (functions as designed or reduced performance);
 egress system (capacity and facility as designed or reduced);
 structural members (perform as designed or reduced performance).
5.2.6 Step 5 — Occupant response

Identify occupant characteristic and response features which are likely to have a significant impact on the course of

the fire. Typical factors for consideration are:
 occupant response to alarm system (normal or delayed response);
 occupant intervention (successful or unsuccessful intervention).
5.2.7 Step 6 — Event tree

Construct an event tree that represents the possible states of the factors that have been identified as significant. A

path through this tree represents a fire scenario for consideration.

Event trees are constructed by starting with an initial state, such as ignition, and then a fork is constructed and

branches added to reflect each possible state of the next factor. This process is repeated until all possible states

have been linked. Each fork is constructed on the basis of occurrence of the preceding state. An example of an

event tree is illustrated in Figure 1 (not all scenarios need to be quantified).
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
Factor 1 Factor 2 Factor 3 Factor 4 OUTCOME
State1 Scenario 1
State1
State 2 Scenario 2
State1
State1 Scenario 3
State 2
State 2 Scenario 4
State1 Scenario 5
State1
State 2 Scenario 6
State 1 State 2
State1 Scenario 7
State 2
State 2 Scenario 8
State1 Scenario 9
State1
State 2 Scenario 10
State 3
State1 Scenario 11
State 2
State 2 Scenario 12
Fire event
State1 Scenario 13
State1
State 2 Scenario 14
State1
State1 Scenario 15
State 2
State 2 Scenario 16
State1 Scenario 17
State1
State 2 Scenario 18
State 2 State 2
State1 Scenario 19
State 2
State 2 Scenario 20
State1 Scenario 21
State1
State 2 Scenario 22
State 3
State1 Scenario 23
State 2
State 2 Scenario 24
Figure 1 — Example of an event tree
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
5.2.8 Step 7 — Consideration of probability

Estimate the probability of occurrence of each state using available reliability data and/or engineering judgement.

These can be marked on the event tree.

Evaluate the relative probability of each scenario by multiplying all the probabilities along the path leading to the

scenario.
5.2.9 Step 8 — Consideration of consequences

Estimate the consequences of each scenario using engineering judgement. The consequences should be

expressed in terms of an appropriate measure such as life loss, likely number of injuries or fire cost. The estimates

should be conservative and may consider time-dependent effects.
5.2.10 Step 9 — Risk ranking

Rank the scenarios in order of relative risk. The relative risk is calculated by multiplying the measure of the

consequences (step 8) by the probability of occurrence (step 7) of the scenario.
5.2.11 Step 10 — Final selection and documentation

Select the highest-ranked fire scenarios for quantitative analysis. The selected scenarios should represent the

major portion of the cumulative risk (sum of the risk of all scenarios). Input from the regulatory authorities and the

QDR team into this selection process is recommended. For a rigorous analysis, all scenarios in the event tree may

need to be analysed.

Document the fire scenarios selected for analysis. These will become the “design fire scenarios”.

6 Design fires
6.1 Role of design fires in fire safety engineering

Following identification of the design fire scenarios, it is necessary to describe the assumed characteristics of the

fire on which the scenario quantification will be based. These assumed fire characteristics are referred to as “the

design fire”.

The design fire needs to be appropriate to the objectives of the fire safety engineering task. For example, if the

objective is to evaluate the smoke control system, a design fire should be selected that challenges the system. If the

severity of the design fire is underestimated, then the application of engineering methods to predict the effects of the

fire elsewhere may produce results which do not accurately reflect the true impact of the fire and may

underestimate the hazard. Conversely, if the severity is overestimated, unnecessary expense may result.

It needs to be understood that the design fire is unlikely to occur in practice. Actual fires are likely to be less severe

and will not necessary follow the specified design curve, such as a particular heat release rate curve. The design

fire quantification process should thus result in a design profile that is conservative.

6.2 Characteristics of design fires

Design fires are usually characterised in terms of the following variables with respect to time (as needed by the

analysis):
 heat release rate;
 toxic-species production rate;
 smoke production rate;
 fire size (including flame length);
 time to key events such as flashover.
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)

Other variables such as temperature, emissivity and location may be required for particular types of numerical

analysis.

It is possible to have more than one design fire for a particular fire scenario. For example, when fire spreads beyond

the room of fire origin to another enclosure a new design fire may be required to represent the fire in the second

enclosure.

Fire may grow from ignition through to a fully developed stage and finally decay and eventually burn out. The fire is

described by the instantaneous value of the above variables over the life of the fire.

A full specification of a design fire (see Figure 2) may include the following phases:

 incipient phase — characterised by a variety of sources, which may be smouldering, flaming or radiant;

 growth phase — covering the fire propagation period up to flashover or full fuel involvement;

 fully developed phase — characterised by a substantially steady burning rate as may occur in ventilation or

fuel-bed-controlled fires;
 decay phase — covering the period of declining fire severity;
 extinction — when there is no more energy being produced.
Figure 2 — Example of design fire
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SIST ISO/TR 13387-2:2001
© ISO
ISO/TR 13387-2:1999(E)
6.3 Characteristic fire growth

The factors determining the characteristic rate of fire growth for flaming fires are described in ISO/TR 13387-1 and

in references [1] and [2]; th
...

TECHNICAL ISO/TR
REPORT 13387-2
First edition
1999-10-15
Fire safety engineering —
Part 2:
Design fire scenarios and design fires
Ingénierie de la sécurité contre l'incendie —
Partie 2: Conception des scénarios-incendie et des feux
Reference number
ISO/TR 13387-2:1999(E)
---------------------- Page: 1 ----------------------
ISO/TR 13387-2:1999(E)
Contents

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

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

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

4 Symbols and abbreviated terms ............................................................................................................................2

5 Design fire scenarios...............................................................................................................................................3

5.1 Role of design fire scenarios in fire safety design............................................................................................3

5.2 Identification of important design fire scenarios ..............................................................................................4

6 Design fires ..............................................................................................................................................................8

6.1 Role of design fires in fire safety engineering...................................................................................................8

6.2 Characteristics of design fires ............................................................................................................................8

6.3 Characteristic fire growth ..................................................................................................................................10

6.4 Events modifying the design fire ......................................................................................................................10

6.5 Pre-flashover design fires..................................................................................................................................11

6.6 Fully developed fires ..........................................................................................................................................13

6.7 External design fires...........................................................................................................................................15

Annex A (informative) Typical fire growth categories ...........................................................................................16

Bibliography..............................................................................................................................................................17

© 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 13387-2:1999(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 13387-2, 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
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© ISO
ISO/TR 13387-2:1999(E)
Introduction

The specification of appropriate design fire scenarios and design fires are a crucial aspect of fire safety design. The

assumptions made with regard to these factors have a major impact on all aspects of the design as they represent

the input into most of the quantification processes.

A design fire scenario is the description of the course of a particular fire with respect to time and space. It includes

the impact on the fire of building features, occupants, fire safety systems and all other factors. It would typically

define the ignition source and process, the growth of fire on the first item ignited, the spread of fire, the interaction of

the fire with its environment and its decay and extinction. It also includes the interaction of this fire with the building

occupants and the interaction with the features and fire safety systems within the building.

ISO/TR 13387-1 provides a framework for the quantitative fire safety engineering assessment of buildings using

time-dependent calculations. Fire scenario analysis forms the basis of the method described.

The basis of these calculations is the design fire. A design fire is an idealisation of real fires that may occur in the

building. Design fires are described in terms of the variation with time of variables used in the quantitative analysis.

These variables typically include heat release rate, fire size, yield of toxic species and yield of soot.

Where the calculation methods used are not able to predict fire growth and spread to other objects within the

compartment of origin or beyond, such growth and spread needs to be specified by the analyst as part of the design

fire, satisfying the functions of both SS2 and SS3.
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TECHNICAL REPORT © ISO ISO/TR 13387-2:1999(E)
Fire safety engineering —
Part 2:
Design fire scenarios and design fires
1 Scope

This part of ISO/TR 13387 provides guidance on the identification of appropriate design fire scenarios for

consideration in fire safety design. It also provides guidance on the specification of design fires for quantitative

analysis in fire safety design of buildings. This approach may be applied to other constructions. It is intended for use

in conjunction with the methodology outlined in part 1 of this Technical Report.

The document describes a systematic approach to the identification of significant fire scenarios that need to be

considered in fire safety design. Once significant fire scenarios have been identified, the document provides

guidance on the selection of "design fire scenarios“ for quantitative analysis.

The document provides guidance on the specification of "design fires“ to reflect the design fire scenarios that have

been identified for analysis. Design fires are specified in terms of important characteristics that form the input data

into the quantitative analysis of various subsystems of the fire safety system as described in part 1.

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/TR 13387-1, Fire safety engineering — Part 1: Application of fire performance concepts to design objectives.

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.

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 13943, Fire safety — Vocabulary.
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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
design fire

a quantitative description of assumed fire characteristics within the design fire scenario

Typically, it is an idealised description of the variation with time of important fire variables such as heat release rate,

fire propagation, smoke and toxic species yield and temperature.
3.2
design fire scenario
a specific fire scenario on which an analysis will be conducted
3.3
engineering judgement

the process exercised by a professional who is qualified by way of education, experience and recognised skills to

complement, supplement, accept or reject elements of a quantitative analysis
3.4
fire scenario

a qualitative description of the course of a fire with time, identifying key events that characterise the fire and

differentiate it from other possible fires

It typically defines the ignition and fire growth process, the fully developed stage and the decay stage, together with

the building environment and systems that will impact on the course of the fire.
3.5
relative risk
the relative potential for realisation of an unwanted event

It is the product of the probability of occurrence of a consequence and the magnitude of the consequence based on

numbers that are only internally consistent within the set being compared and does not represent the actual risk in

absolute values.
4 Symbols and abbreviated terms
A Area of window opening, expressed in m
g Acceleration due to gravity, expressed in m/s
h Height of window, expressed in m
Q Heat release rate, expressed in MW
m Rate of inflow of air, expressed in kg/s
air
m Rate of volatilisation of fuel, expressed in kg/s
R Burning rate (wood equivalent) , expressed in kg/s
r Stoichiometric air/fuel ratio
rDensity, expressed in kg/m
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t Time, expressed in s, min or h
T Ambient temperature, expressed in °C
T Fire gas temperature, expressed in °C
T Temperature of fire at window, expressed in °C
T Flame temperature along the vertical axis, expressed in °C
w Aggregate window width of enclosure, expressed in m
X Flame length along axis of flame, expressed in m
z Vertical distance, expressed in m
z Flame height, expressed in m
5 Design fire scenarios
5.1 Role of design fire scenarios in fire safety design

Design fire scenarios are at the core of the fire safety engineering methodology described in all parts of

ISO/TR 13387. The methodology is based on 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 set. Identification of the appropriate scenarios requiring analysis is crucial to the attainment of a building

that fulfils the fire safety performance objectives.

In reality, the number of possible fire scenarios in most buildings approaches infinity. It would be impossible to

analyse all scenarios even with the aid of the most sophisticated computing resources. This infinite set of

possibilities needs to be reduced to a finite set of design fire scenarios that are amenable to analysis and the results

of which represent an acceptable upper limit to the fire risk. That is to say that more onerous fire scenarios have an

acceptable probability of occurring and that the consequences of those scenarios would need to be borne by

society. The outcome of these extreme scenarios may be mitigated by additional factors that are often outside the

scope of the analysis. Regulatory authority input into, and concurrence with, the selection of the design fire

scenarios is most desirable.

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

each of the fire safety subsystems, different internal ventilation conditions and different external environmental

conditions. The possible consequences of each design fire scenario need to be considered.

Important design fire scenarios need to be identified during the qualitative design review (QDR) stage. During this

process, it is possible to eliminate scenarios that are of low consequence or have a very low probability of

occurrence from further consideration (see 5.2.4). It is important to remember that smouldering fires may have the

potential to cause a large number of fatalities in certain occupancies such as residential buildings.

Each design fire scenario is represented by a unique occurrence of events and is the result of a particular set of

circumstances associated with the fire safety measures. Accordingly, a design fire scenario represents a particular

combination of outcomes or events associated with factors such as:
 type of fire;
 internal ventilation conditions;
 external environmental conditions;
 performance of each of the fire safety measures;
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 type, size and location of ignition source;
 distribution and type of fuel;
 fire load density;
fire suppression;
 state of doors;
 breakage of windows;
 building air-handling system.

Design fires may be needed for a wide range of design fire scenarios. These may be internal or external fire

scenarios. Examples of typical design fire scenarios include:
a) Internal
 room fire (corner, ceiling, floor, wall);
 fire in stairwells;
 single burning item fire (furniture, wastepaper basket, fittings);
 developing fire (smoke extraction);
 cable tray or duct fire;
 roof fires (under roof);
 cavity fire (wall cavity, facade, plenum).
b) External
 fire in neighbouring building;
 fires in external fuel packages;
 fires on roofs;
 fires on facades.

Other design fire scenarios may be agreed upon during the QDR for special situations.

5.2 Identification of important design fire scenarios
5.2.1 General

A systematic approach to the identification of fire scenarios for analysis is desirable in order to identify all important

scenarios and to provide a consistent approach by different analysts.

Generally, several design fire scenarios must be applied to the building under consideration to meet different

requirements. At least one fire scenario should be considered for structural hazards and one for life safety hazards.

A risk-ranking process is recommended as the most appropriate basis for the selection of design fire scenarios.

Such a process takes into account both the consequences and likelihood of the scenario.

Key aspects of the risk-ranking process, explained in the detailed steps below, are:

 identification of a comprehensive set of possible fire scenarios;
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 estimation of the probability of occurrence of the scenario using available data and engineering judgement;

 estimation of the consequence of the scenario using engineering judgement;

 estimation of the relative risk of the scenarios (product of consequence and probability of occurrence);

ranking of the fire scenarios according to the relative risk.

Design fire scenarios may need to consider not only the impact of all of the fire safety provisions on the chosen

design fire but also the partial or complete failure of fire safety provisions.

Generally, fire scenarios involving simultaneous failure of a number of reliable fire safety systems properly

maintained need not be considered as the combined probability of such scenarios are very low. However, if they are

associated with very severe consequences, where the resultant risk is significant, then they need to be considered.

Fire incident statistics provide an appropriate basis for identification of the initial set of possible design fire

scenarios. Fire statistics can be used to identify both the most common types of fire as well as the most hazardous

type of fire for a particular occupancy.

The following systematic approach towards identifying possible design fire scenarios is recommended. It is

recognised that alternative means of identifying design fire scenarios may be used.

5.2.2 Step 1 — Type of fire

From fire incident statistics appropriate for the building and occupancy under consideration, identify:

a) the most likely type of fire scenario;
b) the most likely severe-consequence fire scenario.

The most likely type of fire scenario can be determined from consideration of the items most commonly ignited, the

ignition source and location of the fire from relevant fire incident statistics.

The most likely severe-consequence fire scenario can be determined by consideration of a subset of the fire

incident statistics based upon an appropriate measure of the consequences, such as life loss or property loss. From

this subset of severe-consequence incidents, appropriate for the building and occupancy under consideration, the

most likely severe-consequence fire scenario can be identified.

If appropriate national statistics are not available, then information from other countries with similar fire experience

may be utilised. Care needs to be exercised in applying fire incident statistics to ensure that the data is appropriate

for the building under consideration.
5.2.3 Step 2 — Location of fire

For each of the scenarios identified in step 1, select a specific location or locations in the building that would

produce the most adverse fire scenario(s).
5.2.4 Step 3 — Potential fire hazards

Consider the fire scenarios that could arise from the potential fire hazards identified during the qualitative design

review phase.

Identify other critical severe-consequence scenarios for consideration. These scenarios typically involve:

 fires in assembly areas;
 fires within the egress system;
 fires blocking entry into the egress system;
 fires leading to structural collapse;
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 fires involving high-hazard materials;
 fires exhibiting rapid growth.

If any of these scenarios is likely to have more severe consequences than those identified previously, they need to

be included in the set for analysis. They may replace less hazardous scenarios that are similar in nature.

5.2.5 Step 4 — Systems impacting on fire

Identify the building and fire safety system features which are likely to have a significant impact on the course of the

fire or the development of untenable conditions. Typical factors for consideration and their states include:

 type of fire (smouldering or flaming);
 wind (calm or representative of the location);
 doors and other openings in the enclosure of fire origin (open or closed);
 active suppression system (successful or unsuccessful in controlling fire);
 smoke management system (performed as expected or reduced performance);
 windows (glass intact or glass breaks);
 fire detection system (functions as designed or reduced performance);
 materials control (effective in limiting fire growth or not);

 warning and communication system (functions as designed or reduced performance);

 compartmentation (functions as designed or reduced performance);
 egress system (capacity and facility as designed or reduced);
 structural members (perform as designed or reduced performance).
5.2.6 Step 5 — Occupant response

Identify occupant characteristic and response features which are likely to have a significant impact on the course of

the fire. Typical factors for consideration are:
 occupant response to alarm system (normal or delayed response);
 occupant intervention (successful or unsuccessful intervention).
5.2.7 Step 6 — Event tree

Construct an event tree that represents the possible states of the factors that have been identified as significant. A

path through this tree represents a fire scenario for consideration.

Event trees are constructed by starting with an initial state, such as ignition, and then a fork is constructed and

branches added to reflect each possible state of the next factor. This process is repeated until all possible states

have been linked. Each fork is constructed on the basis of occurrence of the preceding state. An example of an

event tree is illustrated in Figure 1 (not all scenarios need to be quantified).
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Factor 1 Factor 2 Factor 3 Factor 4 OUTCOME
State1 Scenario 1
State1
State 2 Scenario 2
State1
State1 Scenario 3
State 2
State 2 Scenario 4
State1 Scenario 5
State1
State 2 Scenario 6
State 1 State 2
State1 Scenario 7
State 2
State 2 Scenario 8
State1 Scenario 9
State1
State 2 Scenario 10
State 3
State1 Scenario 11
State 2
State 2 Scenario 12
Fire event
State1 Scenario 13
State1
State 2 Scenario 14
State1
State1 Scenario 15
State 2
State 2 Scenario 16
State1 Scenario 17
State1
State 2 Scenario 18
State 2 State 2
State1 Scenario 19
State 2
State 2 Scenario 20
State1 Scenario 21
State1
State 2 Scenario 22
State 3
State1 Scenario 23
State 2
State 2 Scenario 24
Figure 1 — Example of an event tree
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5.2.8 Step 7 — Consideration of probability

Estimate the probability of occurrence of each state using available reliability data and/or engineering judgement.

These can be marked on the event tree.

Evaluate the relative probability of each scenario by multiplying all the probabilities along the path leading to the

scenario.
5.2.9 Step 8 — Consideration of consequences

Estimate the consequences of each scenario using engineering judgement. The consequences should be

expressed in terms of an appropriate measure such as life loss, likely number of injuries or fire cost. The estimates

should be conservative and may consider time-dependent effects.
5.2.10 Step 9 — Risk ranking

Rank the scenarios in order of relative risk. The relative risk is calculated by multiplying the measure of the

consequences (step 8) by the probability of occurrence (step 7) of the scenario.
5.2.11 Step 10 — Final selection and documentation

Select the highest-ranked fire scenarios for quantitative analysis. The selected scenarios should represent the

major portion of the cumulative risk (sum of the risk of all scenarios). Input from the regulatory authorities and the

QDR team into this selection process is recommended. For a rigorous analysis, all scenarios in the event tree may

need to be analysed.

Document the fire scenarios selected for analysis. These will become the “design fire scenarios”.

6 Design fires
6.1 Role of design fires in fire safety engineering

Following identification of the design fire scenarios, it is necessary to describe the assumed characteristics of the

fire on which the scenario quantification will be based. These assumed fire characteristics are referred to as “the

design fire”.

The design fire needs to be appropriate to the objectives of the fire safety engineering task. For example, if the

objective is to evaluate the smoke control system, a design fire should be selected that challenges the system. If the

severity of the design fire is underestimated, then the application of engineering methods to predict the effects of the

fire elsewhere may produce results which do not accurately reflect the true impact of the fire and may

underestimate the hazard. Conversely, if the severity is overestimated, unnecessary expense may result.

It needs to be understood that the design fire is unlikely to occur in practice. Actual fires are likely to be less severe

and will not necessary follow the specified design curve, such as a particular heat release rate curve. The design

fire quantification process should thus result in a design profile that is conservative.

6.2 Characteristics of design fires

Design fires are usually characterised in terms of the following variables with respect to time (as needed by the

analysis):
 heat release rate;
 toxic-species production rate;
 smoke production rate;
 fire size (including flame length);
 time to key events such as flashover.
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Other variables such as temperature, emissivity and location may be required for particular types of numerical

analysis.

It is possible to have more than one design fire for a particular fire scenario. For example, when fire spreads beyond

the room of fire origin to another enclosure a new design fire may be required to represent the fire in the second

enclosure.

Fire may grow from ignition through to a fully developed stage and finally decay and eventually burn out. The fire is

described by the instantaneous value of the above variables over the life of the fire.

A full specification of a design fire (see Figure 2) may include the following phases:

 incipient phase — characterised by a variety of sources, which may be smouldering, flaming or radiant;

 growth phase — covering the fire propagation period up to flashover or full fuel involvement;

 fully developed phase — characterised by a substantially steady burning rate as may occur in ventilation or

fuel-bed-controlled fires;
 decay phase — covering the period of declining fire severity;
 extinction — when there is no more energy being produced.
Figure 2 — Example of design fire
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6.3 Characteristic fire growth

The factors determining the characteristic rate of fire growth for flaming fires are described in ISO/TR 13387-1 and

in references [1] and [2]; they include:
 nature of combustibles;
 geometric arrangement of the fuel;
 geometry of the enclosure;
 ignitability of the fuel;
 rate of heat release characteristics;
 ventilation;
 external heat flux;
 exposed surface area.

Determination of the rate of initial fire growth needs to consider these aspects. Fire models are available that can

predict the rate of fire growth for simple fuel geometries under defined conditions. Experimental data is also

[2]

available to assist in the determination of the rate of fire growth of typical fuel packages.

NOTE The outcome of many design fire scenarios is sensitive to the choice of design fire, in particular the rate of fire

growth.
6.4 Events modifying the design fire
6.4.1 General

The design fire is initially defined in terms of the design fire scenario being analysed. The design fire characteristics

may be subsequently modified based upon the outcome of the analysis (SS1 and SS2). For example, when the fire

has grown to an intensity when flashover in the enclosure is likely, the design fire is modified to reflect the

...

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