ISO 6021:2024

Firebrand generator

This document specifies rules and requirements concerning the construction and operation of a firebrand generator. This document is applicable to all firebrand generators.

General Information

• Status: Published
• Publication Date: 13-Mar-2024
• ICS: 13.220.01 - Protection against fire in general
• Technical Committee: ISO/TC 92 - Fire safety
• Drafting Committee: ISO/TC 92 - Fire safety
• Current Stage: 6060 - International Standard published
• Start Date: 14-Mar-2024
• Due Date: 11-Jan-2024
• Completion Date: 14-Mar-2024

Overview

ISO 6021:2024 - Firebrand generator specifies rules and requirements for the construction and operation of firebrand generators. Intended as an internationally harmonized solution, the standard describes a stand‑alone, reproducible device (reduced‑scale and full‑scale concepts) that produces controlled, continuous firebrand showers for laboratory and experimental testing. It addresses the need to replicate firebrand transport and ignition phenomena observed in large outdoor fires, including wildland‑urban interface (WUI) and urban fire scenarios.

Key topics and technical requirements

• Scope and terminology: Defines key terms (firebrand, spot fire, wildland fire, WUI) aligning with ISO 13943 vocabulary.
• Device description: The ISO Standard Firebrand Generator comprises a stainless‑steel main body and a continuous feeding component with alternating gates, a conveyor, mesh support, blower and handheld propane burner.
• Principles of operation: Continuous feeding of wood pieces produces a distribution of firebrands; blower speed controls glowing versus flaming firebrand showers. The generator can be adapted for wind‑tunnel or wind‑facility testing.
• Operation parameters (examples provided in standard): conveyor speed, feed spacing and feed rate; sample fuel dimensions and mesh support; blower power/velocity guidance; burner/flame configuration. (The standard contains specific measured values and guidance for reproducible settings.)
• Reproducibility and validation: Both reduced‑scale and full‑scale designs have been reproduced by independent laboratories; the number and mass flux of firebrands are to be determined according to feed conditions.
• Alternative methods: Annex A reviews other firebrand generation approaches and situates the standard generator within test practice.

Applications and users

• Practical uses:
  • Laboratory simulation of firebrand showers for material and assembly testing (roofing, decking, walls, mulch, vegetation).
  • Research into firebrand transport, accumulation and ignition of structures in WUI and large outdoor fires.
  • Development and validation of fire‑resistant construction systems and mitigation measures.
• Who should use ISO 6021:2024:
  • Fire safety researchers and universities
  • Test laboratories and certification bodies
  • Fire protection engineers and product manufacturers (roofing, cladding, decking)
  • Emergency planners, regulators and authorities having jurisdiction concerned with wildfire resilience

Related standards

• ISO 13943 (Fire safety - Vocabulary) - normative reference used for terminology.
• Other referenced ISO technical reports and guidance on WUI and outdoor fire behavior (as cited within the document).

Keywords: ISO 6021, firebrand generator, firebrand showers, fire testing, WUI, wildland‑urban interface, fire safety standards, firebrand generation.

Standards Content (Sample)

International
Standard
ISO 6021
First edition
Firebrand generator
2024-03
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
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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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.

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
...