ISO 6021:2024

International
Standard
ISO 6021
First edition
Firebrand generator
2024-03
Reference number
© ISO 2024
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Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Importance of firebrand showers on ignition processes . 2
5 Experimentally simulated firebrand showers . 3
5.1 General .3
5.2 Description of an ISO Standard Firebrand Generator .3
5.2.1 General .3
5.2.2 Principles of operation of the ISO Standard Firebrand Generator .4
6 Operation requirements and guidance . 6
7 Reproducibility . 7
Annex A (informative) Alternative methods of firebrand generation . 8
Bibliography . 9

iii
Foreword
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iv
Introduction
Large outdoor fires present a risk to the built environment. Wildfires that spread into communities, known as
wildland-urban interface (WUI) fires, have destroyed communities throughout the world and are a growing
problem in fire safety science. Another example of large outdoor fires are large urban fires, including those
that can occur after earthquakes. Over the past several decades, fire safety science research has invested a
great deal of effort into understanding fire dynamics within buildings. However, research into large outdoor
fires, and how to potentially mitigate the loss of structures in such fires, lags behind other areas of fire safety
science research. Once a wildland fire reaches a community and ignites structures, structure-structure fire
spread can occur under similar mechanisms as in urban fire spread. Firebrand showers are a main driver of
fire spread in large outdoor fires but there is no accepted internationally harmonized device for generating
firebrand showers. The purpose of this document is to provide a solution for such harmonization. The
firebrand generator described in this document is a stand-alone device.

v
International Standard ISO 6021:2024(en)
Firebrand generator
1 Scope
This document specifies rules and requirements concerning the construction and operation of a firebrand
generator. This document is applicable to all firebrand generators.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain 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
firebrand
airborne object capable of acting as an ignition source and carried for some distance in an airstream
Note 1 to entry: For further information, see Reference [18].
3.2
forest fire
unwanted fire burning forests and wildlands
Note 1 to entry: This term is used primarily, but not exclusively, in Europe.
Note 2 to entry: This term is defined in France as a fire that has reached forests, heaths, underbrush vegetation or
scrub with an area of at least 1 hectare, regardless of the area travelled.
[SOURCE: References [20] and [21], modified — original texts have been restructured to fit ISO format.]
3.3
informal settlement
unplanned settlement and area where housing is not in compliance with current planning and building
[19]
regulations (unauthorized housing)[SOURCE: UN Glossary of Environment Statistics]
3.4
spot fire
fire caused by flying firebrands at a distance from the original fire
[SOURCE: ISO/TR 24188:2022, 3.1.9]

3.5
urban fire
fire which occurs in an urbanized area
[SOURCE: ISO/TR 24188:2022, 3.1.11]
3.6
wildland fire
fire occurring in peat, forests, scrublands, grasslands or rangelands, either of natural origin or caused by
human intervention
Note 1 to entry: This term is 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]
3.7
wildland-urban interface
WUI
area where structures and other human development adjoin or overlap with wildland
[SOURCE: ISO/TS 19677:2019, 3.4]
3.8
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 willdland-urban interface (WUI) and spread into the wildland.
[SOURCE: ISO/TR 24188:2022]
4 Importance of firebrand showers on ignition processes
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
[1],[2],[3]
well-defined boundaries, as is the case in traditional building or enclosure fires. Ignition can occur in
[4]
three ways.
1) Direct flame contact.
2) Thermal radiation: the probability of ignition depends on the distance and on the time of exposure. This
can occur at distances of tenths of metres (dm).
3) Firebrands: the probability of ignition depends on the accumulation. This can occur at long distances
(several hundred metres).
[1],[2],[3],[4]
Firebrand processes have been extensively reviewed. Physical aspects of the firebrand processes
are shown in Figure 1.
a j
Firebrand generation. Smoldering ignition.
b k
Firebrand transport and thermochemical changes. Flaming ignition.
c l
Ignition of target fuel. No ignition.
d m
Firebrand broken off by wind and/or fire-generated plume. Wind.
e
Lofting by buoyant fire plume.
f
Heating from flame or smoldering/glowing reactions.
g
Drag force from relative motion with wind.
h
Convective and radiative cooling.
i
Gravity.
Figure 1 — Firebrand processes in large outdoor fires
5 Experimentally simulated firebrand showers
5.1 General
A major challenge in understanding firebrand transport and ignition is related to showers of firebrands that
are generated in actual large outdoor fires. While studying the fundamental ignition processes of individual
firebrands is important, these studies are not able to quantify the vulnerabilities of structures to ignition
from firebrand showers or to elucidate the physics of firebrand transport. To accomplish this measurement,
methods are required that are capable of replicating firebrand showers that occur in actual large outdoor
fire events. In particular, well-controlled firebrand showers that can be produced
...