Large outdoor fires and the built environment — Global overview of different approaches to standardization

This document provides a review of global testing methodologies related to the vulnerabilities of buildings from large outdoor fire exposures. It also provides information on land use management practices. Some of the test methods outlined in this document have been developed in the context of building fires and extrapolated to external fire exposures.

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TECHNICAL ISO/TR
REPORT 24188
First edition
2022-06
Large outdoor fires and the built
environment — Global overview
of different approaches to
standardization
Reference number
ISO/TR 24188:2022(E)
© ISO 2022
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ISO/TR 24188:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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Published in Switzerland
© ISO 2022 – All rights reserved
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ISO/TR 24188:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

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

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

3 Terms and definitions .................................................................................................................................................................................... 1

4 Ignition scenarios ...............................................................................................................................................................................................3

5 Regulation principle and strategies ................................................................................................................................................ 4

5.1 Japan ................................................................................................................................................................................................................ 4

5.2 California State Building Code (US) ..................................................................................................................................... 5

5.3 NFPA 1144, Standard for Reducing Structure Ignition Hazards from Wildland Fire

(US) ................................................................................................................................................................................................................... 5

5.4 International Wildland Urban Interface Code (IWUIC) ..................................................................................... 5

5.5 France ............................................................................................................................................................................................................. 6

5.6 Australia ....................................................................................................................................................................................................... 6

6 Approach for roofing assemblies .......................................................................................................................................................6

6.1 Japan ................................................................................................................................................................................................................ 6

6.2 North America......................................................................................................................................................................................... 7

6.3 France ............................................................................................................................................................................................................. 7

6.4 Australia ....................................................................................................................................................................................................... 7

7 Approach for exterior walls and facades ................................................................................................................................... 8

7.1 Japan ................................................................................................................................................................................................................ 8

7.2 North America......................................................................................................................................................................................... 8

7.2.1 Fire resistance for exterior walls based on traditional inside-building fire

test methods ........................................................................................................................................................................... 8

7.2.2 Exterior walls outdoor fire exposures............................................................................................................ 8

7.3 France ............................................................................................................................................................................................................. 9

7.4 Australia ....................................................................................................................................................................................................... 9

8 Other building elements .............................................................................................................................................................................. 9

8.1 Vents ................................................................................................................................................................................................................ 9

8.2 Decks ............................................................................................................................................................................................................ 10

8.3 Eaves ............................................................................................................................................................................................................. 10

8.4 Windows.................................................................................................................................................................................................... 10

8.4.1 North America ................................................................................................................................................................... 10

8.4.2 Australia ................................................................................................................................................................................. 10

9 Additional provisions ..................................................................................................................................................................................10

9.1 Reaction-to-fire — California ................................................................................................................................................. 10

9.2 Reaction-to-fire — France......................................................................................................................................................... 11

10 Summary of scenarios and tests ......................................................................................................................................................11

Annex A (informative) Precise description of tests for roof performance defined in the

European Standard CEN/TS 1187 ...................................................................................................................................................14

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

iii
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ISO/TR 24188:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/TR 24188:2022(E)
Introduction

Large outdoor fires have the potential to negatively impact the built environment.

Examples of such fires are:

— wildland-urban interface (WUI) fires (wildland fires that spread into communities; this type of fire

has become a global problem);
NOTE Once a WUI reaches a community, a large urban fire can develop.

— post-earthquake fires (large urban fires that potentially occur after an earthquake);

— tsunami-generated fires (fires potentially generated from tsunamis);

— volcano-generated fires (fires potentially generated from volcanic activity); and

— fires that occur in informal settlements.

This document provides an overview of approaches to standardization for lessening the destruction on

the built environment caused by such fire exposure. Evacuation is not included as there are no known

approaches to standardization as the present time.
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TECHNICAL REPORT ISO/TR 24188:2022(E)
Large outdoor fires and the built environment — Global
overview of different approaches to standardization
1 Scope

This document provides a review of global testing methodologies related to the vulnerabilities of

buildings from large outdoor fire exposures. It also provides information on land use management

practices. Some of the test methods outlined in this document have been developed in the context of

building fires and extrapolated to external fire exposures.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
bushfire
unplanned fire in a vegetated area, as opposed to an urban area

Note 1 to entry: Used primarily, but not exclusively, in Australia, New Zealand, and Africa.

Note 2 to entry: It is likely that the term was first used in South Africa and is possibly derived from the Dutch

word ‘bosch’ meaning uncultivated land. In Australia the term was first used in the first half of the 19 century.

The term passed into legislation in the first half of the 20 century, first in the Australian Capital Territory

(Bushfire Act, 1936), Western Australia (A Bush Fires Act, 1937) and New South Wales (Bush Fires Act, 1949).

Note 3 to entry: Definition adapted from Reference [42].
3.1.2
direct flame contact
flame impinging on building systems and materials

Note 1 to entry: Direct flame contact is one of the three structure ignition pathways, together with firebrands

and radiant heat.

Note 2 to entry: The flames can come either from the main wildfire flames, from burning elements and

ornamental vegetation surrounding structures, or from adjacent structures.
Note 3 to entry: Definition adapted from Reference [42].
3.1.3
evacuation

dispersal or removal of people from dangerous areas and their arrival at a place of relative safety

Note 1 to entry: Definition taken from Reference [42].
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ISO/TR 24188:2022(E)
3.1.4
post-earthquake fire
fire which occurs after an earthquake
3.1.5
firebrand

airborne object capable of acting as an ignition source and carried for some distance in an airstream

Note 1 to entry: Firebrands are also sometimes referred to as flying brands or brands.

Note 2 to entry: Firebrands are similar to embers but with a slight distinction: ember refers to any small, hot,

carbonaceous particle and when embers have the capability of setting additional fires, they become firebrands.

Note 3 to entry: The aerodynamic properties of firebrands is an important characteristic requiring consideration.

Note 4 to entry: Firebrands or embers can be burning, flaming or smouldering.
Note 5 to entry: Definition adapted from Reference [42].
3.1.7
informal settlement

unplanned settlement or area where housing is not in compliance with current planning and building

regulations (unauthorized housing)

[SOURCE: Glossary of Environment Statistics, Studies in Methods, Series F, No. 67, United Nations, New

York, 1997]
3.1.8
large outdoor fire

urban fire, tsunami-generated fire, volcano-generated fire, WUI fire, wildland fire, or informal

settlement fire, where the total burnout area is significant
3.1.9
spot fire
fire caused by flying firebrands at a distance from the original fire
3.1.10
tsunami-generated fire

fire caused by tsunami, typically by burning elements contained in the flood waters

3.1.11
urban fire
fire which occurs in an urbanized area
3.1.13
volcano-generated fire
fire caused by volcanic eruption
3.1.14
wildland

land that either has never suffered human intervention or has been allowed to return to its natural

state, or that is managed for forestry or ecological purposes
[SOURCE: ISO/TS 19677:2019, 3.2]
3.1.15
wildland fire

fire occurring in peat, forests, scrublands, grasslands or rangelands, either of natural origin or caused

by human intervention
Note 1 to entry: Used primarily, but not exclusively, in North America.

[SOURCE: ISO/TS 19677:2019, 3.3, modified — reference to "peat" added and Note 1 to entry added.]

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ISO/TR 24188:2022(E)
3.1.16
wildland firefighting

suppressive action involving a fire in forests, scrublands, grasslands or rangelands

3.1.17
wildland-urban interface
WUI

area where structures and other human development adjoin or overlap with wildland

[SOURCE: ISO/TS 19677:2019, 3.4]
3.1.18
wildland-urban interface community
WUI community
community where humans and their development meet or intermix with wildland fuel
Note 1 to entry: Definition adapted from Reference [45].
3.1.19
wildland-urban interface fire
WUI fire
wildland fire that has spread into the wildland-urban interface (WUI)

Note 1 to entry: It is also possible for fires to start in the wildland-urban interface (WUI) and spread into the

wildland.
3.1.20
wildland-urban interface firefighting
WUI firefighting

suppressive action involving a fire in the wildland-urban interface (WUI) where the action, tactics and

equipment used can differ from urban firefighting
4 Ignition scenarios

It is important to understand that large outdoor fires involve the interaction of topography, weather,

vegetation and structures. Large outdoor fires differ from enclosure fires in several ways; most notably

the fire spread processes are not limited to well-defined boundaries, as is the case of traditional building

or enclosure fires. Wildland firefighting and WUI firefighting techniques, as well as fire mitigation,

also differ in their nature, application and in terms of the distances involved in such situations. At the

interface, the interaction of buildings, construction products used, and urbanization rules are also key

parameters. Reference [32] gives a good overview of these phenomena. There are three ways in which

ignition can occur:

— Direct flame contact — This is the aspect usually managed by fire tests from building regulations.

— Thermal radiation — The probability of ignition depends on the distance and time of exposure. This

can occur at distances of tenths of meters.

— Firebrands — The probability of ignition depends on the accumulation. Spot fires can occur at long

distances (several hundred meters).

A combination of any of these three points is also possible. Direct flame contact and thermal radiation

act in combination as a flame exists and emits thermal radiation. Direct flame contact and firebrands

can also act in combination while direct flame contact is likely dominant. Thermal radiation and

firebrands can act in combination as shown in Figure 1.
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ISO/TR 24188:2022(E)
Key
1 direct flame contact
2 thermal radiation
3 firebrands
4 thermal radiation and firebrands
Figure 1 — Fire propagation modes in large outdoor fires (from Reference [32])
5 Regulation principle and strategies
5.1 Japan
[25]

The Building Standard Law (BSL) of Japan aims to cover the threat of large urban fires. According

to the BSL, there are two major fire tests conducted in Japan in the context of preventing urban fire

spread: a roof test and a fire resistance test for exterior walls.

The purpose of the BSL is to safeguard the life, health and property of people by providing minimum

standards concerning the site, construction, equipment and use of buildings, and thereby to contribute

to the furtherance of the public welfare. To prevent fires from spreading from one building to the next

and to minimize the occurrence of urban fires, buildings located in "fire protection zones (FPZs)",

"quasi-fire protection zones (QFPZs)", and "cities under Article 22” are required to conform to the BSL.

Figure 2 illustrates the basic philosophy of zoning. While no scientific research has yet been carried out

to determine the efficacy of these regulations, due at least in part to the regulations, large urban fires

are a relatively rare occurrence in Japan today, and are most likely to occur under extreme conditions

(in themselves rare), such as those following a major earthquake or in extremely high winds.

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ISO/TR 24188:2022(E)
Key
1 fire protection zone
2 quasi-fire protection zone
3 city under Article 22
4 station
5 railway
Figure 2 — Zoning concept according to BSL of Japan (from Reference [25])
5.2 California State Building Code (US)

California refers to California Building Code, Title 24, Part 1, Chapter 7A Materials and Construction

Methods for Exterior Wildfire Exposure, as well as Chapter 49, Requirements for Wildland-Urban

Interface Areas. The following California State Fire Marshal (SFM) Test Standards are described: 12-7A-

[6] [20] [18] [14] [21]
1, 12-7A-2, 12-7A-3, 12-7A-4, 12-7A-5.

5.3 NFPA 1144, Standard for Reducing Structure Ignition Hazards from Wildland Fire

(US)
[50]

The National Fire Protection Association (NFPA) published the current edition of NFPA 1144 in

2018. This standard can serve as a model for adoption (in total or with amendment) by local building

codes. The scope of the document ranges from assessing fire hazard in the structure ignition zone to

building design, location and construction. Building components covered include: roof, exterior walls,

openings (including windows and doors), chimneys, and accessory structures. Sample qualitative and

quantitative hazard assessment methodologies are included in the Annex. In the 2022 revision process

[48] [49]

this document is to be combined with NFPA 1141 and NFPA 1143 to form a single document, NFPA

1140.
5.4 International Wildland Urban Interface Code (IWUIC)
[47]

The International Code Council (ICC) published the current edition of the IWUIC in 2018. This model

ranges in scope from water supply and vehicles access to building construction and fire protection

requirements. Appendix sections provide additional information on topics including: vegetation

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ISO/TR 24188:2022(E)

management, fire hazard severity assessment forms and “self-defence mechanisms”. Notable is the

Ignition-Resistance Construction system described in Chapter 5. The system contains three class levels

(Class 1, Class 2 and Class 3) and specifies construction requirements for each. Class 3 requires the

nominally most ignition-resistant materials and construction. Several standards and test methods

from other organizations including ASTM, NFPA and UL are referenced.
5.5 France

The French standards and regulations are mainly dedicated to design (or certification by standard

tests) fire resistance or reaction to fire of construction products against compartment fire or

traditional building fires. Nevertheless, standards or performance requirements concern the design of

[51]

products against external fire. The Eurocode EN-1991-1-2 provides a dedicated external fire curve

(temperature-time) pertinent for exposure of structural construction elements against external flame

coming out from windows of other compartments, but this standard is not used for classification tests.

[37]

The European Standard EN-1363-2 indicates that this curve can be considered for outside fire, but in

practice it is also not employed for classification tests.

For wildland-urban interface (WUI) fires, no standards specify the fire exposure explicitly. Instead,

one finds two different categories of approaching standard tests are reviewed in detail in the following

subclauses:

— tests for some structural elements (roofs and facades essentially) which are ad hoc tests, allowing

to test reaction and resistance to fire with ad hoc fire curves and ad hoc acceptance criteria.

— tests for other structural elements which are tests with standard generic fire curves and acceptance

criteria.
5.6 Australia

The Australian National Construction Code (NCC) has performance provisions that address buildings

that are located in a designated bushfire-prone area (WUI fire-prone area). The NCC has three volumes—

the Building Code of Australia is Volume One and Volume Two and the Plumbing Code of Australia is

[54]

Volume Three. Bushfire areas of the NCC 2019 Volume Two is satisfied if the building is constructed

[52]

in accordance with either 1) AS 3959 or 2) NASH Bushfire Standard — Non-combustible building

[44]

cavity construction in bushfire areas. AS 3959 contains normative reference to the two standards

[9] [8]

in the Australian Standard AS 1530.8.1 and AS 1530.8.2 test standards. The testing standards have

[41]

been applied to roof, wall and other assembly types. Baker et al. provide a comprehensive overview

of the regulatory framework of Australia for interested readers.
6 Approach for roofing assemblies
6.1 Japan

Roof tests in Japan are based on ISO 12468-1, with a minor modification of the size of the cribs placed

on the surface of roof specimens. Different cribs are used for the roofs located in different zones. For

the roof specimens which will be constructed in FPZs and QFPZs, total size of crib is (80 × 80 × 60) mm,

which is composed by lumbers, and each configuration is (19 × 19 × 80) mm. On the other hand, for the

[25]

roof specimens in “Cities under Article 22 of BSL (Building Standard Law)” or “Low-flame-spread

roof area”, lumber is used, where the size is (40 × 40 × 40) mm, which conforms to the specifications

of “Brand B” in ISO 12468-1. This difference on firebrands stems from the assumption that buildings

in FPZs and QFPZs are closely adjacent to each other and can therefore produce larger firebrands than

fires in “Cities under Article 22 of BSL”. Furthermore, the roofs of the buildings located in the FPZ and

QFPZ can be less vulnerable to the attacking of flying firebrands in case of urban fire than those in

“Cities under Article 22 of BSL”. The same criteria are applied when interpreting the results of tests for

all specimens, even when different crib configurations are used. There are three major elements in the

criteria, namely, 1) fire propagation (not reaching to the edge of specimen), 2) integrity (no flame on the

reverse side of the specimen), and 3) defect [no through-hole larger than (10 ×10) mm]. Furthermore,

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ISO/TR 24188:2022(E)

non-combustible roof tiles do not even need to be tested. Recent joint USA/Japan research has shown

[27]
these methods do not simulate firebrand showers seen in large outdoor fires.
6.2 North America

There are a few existing test methods that measure the ability of a roof assembly to resist the passage of

[10]

fire into the attic and spread of fire on the roof surface. In Canada, CAN/ULC-S107 is used to measure

[17] [11]

the roof performance, which follows a similar procedure as ASTM E-108 , UL 790 and NFPA

[12]

276 . During the test the assembly is exposed to flames from a calibrated burner. For combustible

roof decks, a series of burning standard brands and an intermittent flame exposure are also required.

The roof assemblies are classified based on their effectiveness against fire exposure, flammability/

combustibility, and degree of fire protection provided to the roof deck, and propensity to produce

flying brands. They provide three classes, Class A, Class B, and Class C. Class A is the most resistant and

Class C the least resistant. Recent joint US/Japan research has shown these methods do not simulate

[27]
firebrand showers seen in large outdoor fires.
6.3 France
[34]

CEN/TS 1187 is a collection of 4 separate tests, and in France, test 3 is applied. Even if a roof is

validated according to test 3, it is not considered valid in the 3 other tests. Details are provided in

Annex A.

Test 3 has an ad hoc experimental setup, including firebrands positioned at defined positions on the

roof before being flamed, low atmospheric wind conditions (around 3 m/s) possibly propagating the

fire to the roof components, and a radiative heating from a radiant panel at about 12,5 kWm . The

firebrands are composed of 4 pieces of wood assembled together to build a crib of (55 × 55 × 32) mm,

pre-conditioned in temperature and relative humidity. This setup has been initially designed not to

represent wildfire firebrands, but rather to represent burning pieces of timber or construction wooden

items, which have been projected from a neighbouring building fire. A 30 min fire exposure is performed.

[35]

Classification criteria (A, B, … roof) are given by the adjacent standard EN 13501-5 :2005+1 :2009.

Precise details on this test design, as well as comparison with the other tests, are found in Annex A.

6.4 Australia
[8]

AS 1530.8.2 is the Australian test standard for WUI exposure. AS 1530.8.2 is for severe fire exposure

or direct flame impingement (BAL FZ). During AS 1530.8.2, a representative element of construction

or combination of elements is exposed to the standard fire curve. The test duration is 90 min which

includes a 30-min exposure to the standard fire and a 60-min monitoring period.
[9]
For lower e
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