ISO/FDIS 5660-5

• Abstract:

  This document specifies the apparatus and procedure for measuring reaction to fire behaviour under reduced oxygen atmospheres. Continuous measurements are made to calculate heat release rates, smoke and specific gas production rates, and mass loss rates. Ignition time measurements are also made and ignition behaviour is obtained. Pyrolysis parameters of specimens exposed to controlled levels of irradiance and controlled levels of oxygen supply can be determined as well. Different reduced oxygen atmospheres in the test environment are achieved by controlling the oxygen volume concentration of input gas fed into the chamber (vitiation) or by controlling the total volume of atmosphere fed into the chamber (ventilation). Ranges of oxygen volume concentration below 20,95 % of oxygen can be studied. The apparatus is not intended to control enriched oxygen conditions above atmospheric 20,95 % oxygen concentration. The measurement system prescribed in this document is based on the cone calorimeter apparatus described in ISO 5660-1. Therefore, this document is intended to be used in conjunction with ISO 5660-1.

• Status: Not Published
• ICS: 13.220.50 - Fire-resistance of building materials and elements
• Technical Committee: ISO/TC 92/SC 1 - Fire initiation and growth
• Drafting Committee: ISO/TC 92/SC 1/WG 5 - Small and bench scale fire test methods
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 02-Oct-2026
• Completion Date: 02-Oct-2026

• Revises: ISO/TS 5660-5:2020 - Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 5: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement) under reduced oxygen atmospheres
• Effective Date: 24-Feb-2024

Overview

ISO/FDIS 5660-5:2026 is an international standard developed by ISO Technical Committee 92 (Fire Safety) that specifies methods for evaluating the reaction-to-fire performance of materials under reduced oxygen atmospheres. This standard details how to measure heat release rate, smoke production, mass loss rate, specific gas production rates, and ignition times of specimens. The test methods outlined utilize the cone calorimeter approach and are designed to provide deeper insight into material behavior under vitiated (oxygen-depleted) or ventilation-controlled conditions, reflecting real-world fire environments where oxygen concentration is often below the standard 20.95% found in ambient air.

This standard is intended for use in conjunction with ISO 5660-1, as it employs similar apparatus and testing principles, with modifications to facilitate controlled oxygen atmospheres. By controlling both irradiance and oxygen supply, ISO/FDIS 5660-5 enables comprehensive fire testing for a wide range of products and materials across industries where fire risk management is a priority.

Key Topics

• Heat Release Rate Measurement: Using cone calorimetry, the apparatus measures oxygen consumption during combustion to determine the net heat release rate, providing essential information for fire growth modeling.
• Smoke Production and Gas Analysis: The system gauges smoke density and specific gas production rates dynamically, using light transmission and gas sampling techniques, crucial for toxicity and visibility assessments.
• Mass Loss Rate & Pyrolysis: Continuous tracking of sample mass loss offers additional insight into material degradation and burning efficiency under restricted oxygen, supporting safety engineering.
• Reduced Oxygen Atmospheres: The test chamber allows precise control of oxygen concentrations below atmospheric levels, mimicking real fire scenarios and evaluating performance where vitiation or under-ventilation occurs.
• Specimen Preparation & Calibration: The standard addresses specimen construction requirements, calibration of the oxygen analyzer and apparatus, and stringent procedural controls to ensure accurate and repeatable results.

Applications

ISO/FDIS 5660-5 delivers practical value for a diverse range of sectors, such as:

• Building Materials: Evaluating construction products for compliance with reaction-to-fire criteria under real fire conditions, supporting code compliance and building safety.
• Transport: Assessing the fire performance of materials used in ships, trains, aircraft, and road vehicles, where oxygen-depleted conditions may commonly occur.
• Plastics and Polymers: Testing new polymeric materials for ignitability, heat release, and smoke generation under controlled atmospheres, aiding in materials selection and product development.
• Research and Certification: Providing laboratories and regulatory bodies a rigorous methodology for advanced fire testing, leading to improved understanding and safer design solutions.
• Fire Safety Engineering: Supporting modeling of fire growth and smoke movement in compartment fires, particularly in complex environments with oxygen-depleted zones.

Related Standards

• ISO 5660-1:2015+A1:2019 - Reaction-to-fire tests – Heat release, smoke production, and mass loss rate – Part 1: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement).
• ISO 13927:2023 - Plastics – Simple heat release test using a conical radiant heater and a thermopile detector.
• ISO 13943 - Fire safety – Vocabulary.

These related standards facilitate harmonized terminology, apparatus design, and calculation methods across reaction-to-fire testing, ensuring consistency in results and global comparability.

---

Applying ISO/FDIS 5660-5 enhances the reliability of fire testing under reduced oxygen conditions, aligning with international fire safety objectives and supporting the development of safer, more resilient materials and products worldwide.

FINAL DRAFT
International
Standard
ISO/TC 92/SC 1
Reaction-to-fire tests — Heat
Secretariat: BSI
release, smoke production and
Voting begins on:
mass loss rate —
2026-10-02
Part 5:
Voting terminates on:
2026-11-27
Heat release rate (cone calorimeter
method) and smoke production
rate (dynamic measurement) under
reduced oxygen atmospheres
Essais de réaction au feu — Débit calorifique, taux de
dégagement de fumée et taux de perte de masse —
Partie 5: Débit calorifique (méthode au calorimètre à cône) et
taux de dégagement de fumée (mesurage dynamique) dans des
atmosphères pauvres en oxygène
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 92/SC 1
Reaction-to-fire tests — Heat
Secretariat: BSI
release, smoke production and
Voting begins on:
mass loss rate —
Part 5:
Voting terminates on:
Heat release rate (cone calorimeter
method) and smoke production
rate (dynamic measurement) under
reduced oxygen atmospheres
Essais de réaction au feu — Débit calorifique, taux de
dégagement de fumée et taux de perte de masse —
Partie 5: Débit calorifique (méthode au calorimètre à cône) et
taux de dégagement de fumée (mesurage dynamique) dans des
atmosphères pauvres en oxygène
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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 Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope .1
2 Normative references .1
3 Terms and definitions .1
4 Symbols . 2
5 Principle .3
6 Apparatus .4
6.1 General .4
6.2 Heater and enclosure and chimney arrangement with cone calorimeter as per
ISO 5660-1 .6
6.2.1 General .6
6.2.2 Enclosure .6
6.3 Water-cooling for weighing device .8
6.4 Chimney .8
6.5 Air- and gas-supply system .9
6.6 Enclosure oxygen analyser .9
6.7 Data collection and analysis system .9
7 Suitability of product for testing .10
8 Specimen construction and preparation . 10
9 Test environment . 10
10 Calibration .10
10.1 General .10
10.2 Operating calibrations .10
10.2.1 Enclosure oxygen analyser . .10
10.2.2 Enclosure flow rate measurement .10
10.2.3 Heater calibration . . .10
11 Test procedure .10
11.1 General precautions .10
11.2 Initial preparation .11
11.3 Procedure .11
11.3.1 General .11
11.3.2 Pre-test conditions .11
11.4 Criteria to consider a test as successful . 13
12 Calculations .13
12.1 General . 13
12.2 Calibration constant for oxygen consumption analysis . 13
12.3 Correct time delay .14
12.4 Heat release rate .14
13 Test report .15
Annex A (informative) Guidance for operators .16
Annex B (informative) Additional information for using the linked configuration .17
Annex C (informative) Additional information for using the enclosure as standalone device
with ISO 13927 controls .18
Annex D (informative) Gas flow rates .19
Bibliography .25

iii
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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
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, Subcommittee SC 1, Fire
initiation and growth.
This first edition of ISO 5660-5 cancels and replaces ISO/TS 5660-5:2020.
A list of all parts in the ISO 5660 series can be found on the ISO website.
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
Continuous measurements are made to calculate heat release rates, smoke and specific gas production rates,
and mass loss rates. Ignition time measurements are also made and ignition behaviour is obtained. Pyrolysis
parameters of specimens exposed to controlled levels of irradiance and controlled levels of oxygen supply
can be determined as well.
Different reduced oxygen atmospheres in the test environment are achieved by controlling the oxygen volume
concentration of input gas fed into the chamber (vitiation) or by controlling the total volume of atmosphere
fed into the chamber (ventilation). Ranges of oxygen volume concentration below 20,95 % of oxygen can be
studied. The apparatus is not intended to control enriched oxygen conditions above atmospheric 20,95 %
oxygen concentration.
The measurement system prescribed in this document is based on the cone calorimeter apparatus described
in ISO 5660-1. Therefore, this document is intended to be used in conjunction with ISO 5660-1.

v
FINAL DRAFT International Standard ISO/FDIS 5660-5:2026(en)
Reaction-to-fire tests — Heat release, smoke production and
mass loss rate —
Part 5:
Heat release rate (cone calorimeter method) and smoke
production rate (dynamic measurement) under reduced
oxygen atmospheres
1 Scope
This document specifies the apparatus and procedure for measuring reaction to fire behaviour under
reduced oxygen atmospheres. 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.
2 Normative references
ISO 5660-1, Reaction-to-fire tests — Heat release, smoke production and mass loss rate — Part 1: Heat release
rate (cone calorimeter method) and smoke production rate (dynamic measurement)
ISO 13927:2023, Plastics — Simple heat release test using a conical radiant heater and a thermopile detector
ISO 13943, Fire safety — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5660-1, 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
ambient atmosphere
atmosphere with an oxygen volume concentration of approximately 20,95 % in a control volume and
unrestricted air flow into the same control volume
3.2
reduced oxygen atmosphere
vitiated atmosphere or under-ventilated atmosphere that differ from ambient atmospheres
A vitiated atmosphere is an atmosphere with less oxygen molecules than in ambient air in the same volume at same
temperature and pressure levels (oxygen concentration below 20,95 %; vitiated conditions), with the remaining
molecules balanced by inert gas molecules.

Note 1 to entry: An under-ventilated atmosphere is an atmosphere with a limited air supply that leads to fewer oxygen
molecules per time supplied to a combustion reaction than needed to allow stoichiometric reactions to take place
(under-ventilated conditions).
3.3
vitiation-controlled condition
condition under which the volume concentration of oxygen is intentionally controlled or reduced in the
combustion environment
Note 1 to entry: Vitiation-controlled conditions represent an oxygen depleted fire environment.
3.4
ventilation-controlled condition
condition in which the supply rate of (ambient or vitiated) air to the combustion environment is intentionally
controlled or limited
Note 1 to entry: Ventilation-controlled conditions represent a fire environment with limited fresh air supply.
4 Symbols
For the purposes of this document, the symbols given in ISO 5660-1 and the following apply.
initially exposed surface area of the specimen
A m
S
1/2 1/2 1/2
C
orifice flow meter calibration constant m g K
γ
thermal expansion factor —

γ
thermal changeable dilution factor —
−1
net heat of combustion
∆h kJ g
c
−1
 mass flow rate in the exhaust duct during the test kg s
m
e
0 −1
initial mass flow rate in the exhaust duct
kg s

m
e
−1
 mass flow rate of fuel, burning rate of the specimen
m kg s
f
E −1
mass flow rate of the incoming gas mixture to the enclosure
 kg s
m
g
∆p
orifice meter pressure differential Pa
 heat release rate kW
qt

−2
 heat release rate per unit area
qt kW m

A
φ
oxygen depletion factor —
absolute temperature of gas at the orifice meter K
T
e

volume flow rate of air l/min
V
A
E
 volume flow rate of gas to the enclosure
l/min
V
g

volume flow rate of nitrogen gas
V l/min
N
oxygen concentration in air (bottled, pressurized) —
X
O , Air
value of combustion gas oxygen analyser reading, before delay time correction
—
X
O
A
actual value of combustion gas oxygen analyser reading
—
X
O
average of the oxygen analyser output measured during the 1-min initial baseline
A
X —
O
measurement
S
average of the oxygen analyser output measured during the 1-min surroundings
A
X —
O baseline measurements before the enclosure has been supplied with air or gas
A
actual value of combustion gas carbon monoxide analyser reading
—
X
CO
A
actual value of combustion gas carbon dioxide analyser reading
—
X
CO
E
oxygen concentration in the enclosure
X —
O
S
surrounding baseline value of combustion gas carbon dioxide analyser reading
A
X —
CO
(before enclosure environment established – enclosure door open)
S
surrounding value of water vapour
—
X
HO
H relative air humidity of the surrounding before the test %
p ambient pressure of the surrounding before the test Pa
T ambient temperature of the surrounding before the test K
a
5 Principle
The principle of this test method is based on the observation that, generally, both thermal and chemical
products of a combustion reaction vary in quantity and quality depending on the atmospheric environmental
conditions in which the reactions occurs. This test method provides a controlled environment to assess the
contribution that a product under test can make to the rate of heat release, the production rate of gaseous
products and the smoke production rate, in either different reduced oxygen atmospheres or differently
ventilated atmospheres, or both, during the product’s involvement in fire. The properties are determined on
small representative specimens. Specimens in the test are burned in ambient atmospheres or predetermined
reduced oxygen atmospheres, while being subjected to a predetermined external irradiance within the
−2 −2
range of 0 kW m to 50 kW m . Measurements are made of oxygen and other gas concentrations in the
exhaust, light transmission, exhaust gas flow rates and specimen mass.
Heat release rate measurement is based on the observation that the net heat of combustion is proportional
to the amount of oxygen required for combustion. The relationship is that approximately 13,1 × 10 kJ of heat
are released per kilogram of oxygen consumed. This is accurate within ± 5 % for complete combustion and
differs by ±20 % considerably for incomplete combustion. Measurements of oxygen concentrations and total
exhaust gas flow rates are conventionally made. Enhanced measurements of carbon dioxide concentrations,
carbon monoxide concentrations, other species concentrations, soot, water vapour and unburnt fuel allow
application of appropriate corrections depending on stoichiometries of the combustion reactions. These
measurements are used to calculate the mass of oxygen consumed. Results are reported as heat release
rate and total heat release, both normalized to exposed specimen surface area. The heat release rate of a
burning specimen is calculated as the product of the oxygen mass consumed by the fire and the averaged
3 −1
proportionality 13,1 × 10 kJ kg with corrections for incomplete combustion. The enhanced measurements
for carbon dioxide, carbon monoxide and water vapour are applied for general corrections in this document.
Where available, specific values for the proportionality can be used as quotient of the heat of combustion
of a burning fuel and its stochiometric oxygen to fuel mass ratio. The total heat release is calculated by
numerical integration of the heat release rate over the time interval being considered. Both variables are
normalized to area because heat release is proportional to the burning surface area.
The principle of the smoke measurement is based on the observation that, generally, the intensity of light
that is transmitted through a volume of combustion products is an exponentially decreasing function of
distance. Measurements are made of exhaust gas obscuration, exhaust gas flow rate and mass loss rate of

the specimen. Exhaust gas obscuration is measured as the fraction of laser light intensity that is transmitted
through the mixture of gases, aerosols, and particles in the exhaust duct. This fraction is used to calculate
the extinction coefficient according to Bouguer’s law. In particular, with non-flaming and anaerobic
pyrolysis processes, extinction coefficients differ from extinction values for combustion smoke. The test
results are reported in terms of smoke production and smoke production rate, both normalized to exposed
specimen surface area. Smoke production rate is calculated as the product of the extinction coefficient and
the volumetric flow rate of the smoke in the exhaust duct. Smoke production is calculated by numerical
integration of the smoke production rate over the time interval being considered. The variables reported are
normalized to area because smoke production is proportional to area.
Gas production measurements are performed by measuring gas concentrations in the exhaust duct. Gas
production rates are calculated from those concentration measurements utilizing general formulae and
relations. Species yields are derived from the specific gas mass flow rate divided by the actual fuel mass loss
rate at the same time interval.
Atmospheric environmental conditions may range from approximately 1 % to 20,95 % of oxygen and 150 l/
min to 180 l/min volume flow rate (when ventilation-controlled conditions are not intended). They are
predetermined and controlled within the combustion environment by maintaining the ratio and volume
flow rate of air and nitrogen gas respectively. The oxygen concentration in the atmospheric conditions
and the total gas flow rate to the environment are monitored with relevant measurement devices. Air and
nitrogen gas shall be provided either as bottled gases or as oil-free pressurized air from a compressor and
liquid nitrogen vaporizer respectively.
6 Apparatus
6.1 General
The apparatus described in this document allows measurement of reaction to fire behaviour under reduced
oxygen atmospheres. Ranges of oxygen volume concentration below 20,95 % of oxygen can be studied. For
those conditions above 15 % of oxygen, flaming combustion is usually expected. For those below 15 % of
oxygen, flaming can occur but is generally not expected to occur for many products. Anaerobic pyrolysis
experiments at close to 0 % of oxygen can be carried out in absence of the oxygen depletion measurements.
The apparatus utilizes the components and controls of the apparatus specified in ISO 5660-1 supplemented
by apparatus modification detailed in this document to facilitate testing under reduced oxygen atmospheres.
This principally consists of replacing the standard cone heater assembly by a second unit housed in a
chamber that can by supplied with metered mixtures of air and nitrogen. Measurements are otherwise
similar to those made in ISO 5660-1.
The gas measurement equipment detailed in ISO 5660-1 shall be used
An apparatus exclusively for anaerobic pyrolysis experiments may alternatively utilize components and
controls of the apparatus specified in ISO 13927.
A schematic representation of the apparatus required for this document is given in Figure 1. Components
described in ISO 5660-1 are marked. Components specific to reduced oxygen atmosphere testing are
specified in 6.1 to 6.7.
Key
1 exhaust hood
2 exhaust duct
3 sampling ring
4 pressure ports
5 orifice plate
6 thermocouple
7 stack
8 exhaust fan
9 laser extinction beam
10 chimney
11 cone heater
12 radiation shield
13 ignition circuit
14 controlled-atmosphere chamber (enclosure)
15 sample holder and specimen
16 cooled shield
17 weighing device
18 baffles
19 mass flow meter
20 air
21 nitrogen
Figure 1 — Overview of the arrangement of enclosure, chimney and cone calorimeter according to
ISO 5660-1
The conical shaped radiant heater described in ISO 5660-1 shall be integrated into the top face of an
enclosure. The cabinet shall also include the radiation shield, the weighing device with an additional cooling
shield, the specimen holder and the ignition circuit as described in ISO 5660-1. The heat flux meter and
housing and the calibration burner shall also be provided. Appropriate mountings shall be available to
perform calibration measurements using the heat flux meter and calibration inside the enclosure. A gas
mixing and supply system shall be connected to the enclosure to allow adjusting the atmospheric conditions.
6.2 Heater and enclosure and chimney arrangement with cone calorimeter as per
ISO 5660-1
6.2.1 General
The test enclosure described in 6.2.2 replaces the standard cone heater assembly in the ISO 5660-1 apparatus.
It shall be centred underneath the exhaust hood and can be used in each of the following configurations
using a chimney on top of the enclosure as described in 6.4.
a) When testing with an enclosure gas supply rate lower than the exhaust flow rate, the enclosure and
chimney should not be linked directly to the exhaust hood. Air from the surroundings shall be allowed
to enter the exhaust hood.
NOTE 1 The effect of the chimney in the unlinked configuration on various results are discussed in
Reference [2].
NOTE 2 An exhaust flow rate that exceeds the enclosure supply rate would cause under pressure, leakages and
potentially uncontrolled conditions in the enclosure.
b) When undertaking anaerobic pyrolysis experiments these can be carried out in either unlinked (shown
in 6.1) or linked apparatus (Item 2) depending on the applicable gas supply rate or if the enclosure is
stand-alone without the oxygen depletion measurement equipment running. Annex C specifies more
details about the stand-alone arrangement.
Regardless of the configuration or the enclosure inlet gas flow rate, the exhaust flow rate in the duct shall
be sufficiently high to reliably entrain all combustion products released during the process. The minimum
exhaust flow rate at the beginning of the test shall be at least 0,012 ± 0,002 m /s.
6.2.2 Enclosure
A stainless steel enclosure as shown in Figure 2 shall have internal dimensions of W × D × H
of (370 ± 20) mm × (320 ± 20) mm × (330 ± 20) mm. A door shall be mounted on the front of the enclosure
to provide access to all inner parts and to allow specimen loading. When opened for specimen loading, a
door can allow significant amounts of air entering the enclosure. This can unintentionally change the
predetermined controlled atmosphere. An alternative opening scheme may be used if it allows only minimum
air entering the enclosure during specimen loading. At least one wall or door element shall contain a window
to allow the specimen to be observed during a test. At least one gas connection port shall be mounted at the
level of the sample that allows gas sampling of the enclosure atmosphere. Additional ports can be present for
cooling water entry, additional gas sampling or temperature measurement, or all, as well as extinguishing
and radiation measurement equipment.
...

ISO/TC 92/SC 1
Secretariat: BSI
Date: 2026-05-2909-18
Reaction-to-fire tests — Heat release, smoke production and mass
loss rate —
Part 5:
Heat release rate (cone calorimeter method) and smoke production
rate (dynamic measurement) under reduced oxygen atmospheres
Essais de réaction au feu – — Débit calorifique, taux de dégagement de fumée et taux de perte de masse – Partie
5: —
Partie 5: Débit calorifique (méthode au calorimètre à cône) et taux de dégagement de fumée (mesurage
dynamique) dans des atmosphères pauvres en oxygène
FDIS stage
ISO/TS FDIS 5660-5:2020(E2026(en)
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'sISO’s member body in the country of the requester.
ISO Copyright Officecopyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
Email: E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland.
ii
ii
Contents Page
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols . 2
5 Principle . 3
6 Apparatus . 4
6.1 General. 4
6.2 Heater and enclosure and chimney arrangement with cone calorimeter as per ISO 5660-
1 . 6
6.3 Water-cooling for weighing device . 8
6.4 Chimney . 9
6.5 Air- and gas-supply system . 9
6.6 Enclosure oxygen analyser . 10
6.7 Data collection and analysis system . 10
7 Suitability of product for testing . 10
8 Specimen construction and preparation . 10
9 Test environment . 10
10 Calibration . 10
10.1 General. 10
10.2 Operating calibrations . 11
11 Test procedure . 11
11.1 General precautions . 11
11.2 Initial preparation . 11
11.3 Procedure . 11
11.4 Criteria to consider a test as successful . 14
12 Calculations . 14
12.1 General. 14
12.2 Calibration constant for oxygen consumption analysis . 14
12.3 Correct time delay . 15
12.4 Heat release rate . 15
13 Test report . 16
Annex A (informative) Guidance for operators . 18
Annex B (informative) Additional information for using the linked configuration . 19
Annex C (informative) Additional information for using the enclosure as standalone device with
ISO 13927 controls . 20
Annex D (informative) Gas flow rates . 21
Bibliography . 28

iii
ISO/TS FDIS 5660-5:2020(E2026(en)
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 documentsdocument 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 drawnISO draws attention to the possibility that some of the elementsimplementation of this
document may beinvolve the subjectuse of (a) patent(s). ISO takes no position concerning the evidence,
validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO had not received notice of (a) patent(s) which may be required to implement this document.
However, implementers are cautioned that this may not represent the latest information, which may be
obtained from the patent database available at www.iso.org/patents. 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 ).
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
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This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 1, Fire
initiation and growth.
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iv
iv
Introduction
v
Reaction to fire tests — Heat release, smoke production and mass loss
rate — Part 5: Heat release rate (cone calorimeter method) and smoke
production rate (dynamic measurement) under reduced oxygen
atmospheres
1 Scope
This document specifies the apparatus and procedure for measuring reaction to fire behaviour under reduced
oxygen atmospheres. Continuous measurements are made to calculate heat release rates, smoke and specific
gas production rates, and mass loss rates. Ignition time measurements are also made and ignition behaviour
is obtained. Pyrolysis parameters of specimens exposed to controlled levels of irradiance and controlled levels
of oxygen supply can be determined as well.
Different reduced oxygen atmospheres in the test environment are achieved by controlling the oxygen volume
concentration of input gas fed into the chamber (vitiation) or by controlling the total volume of atmosphere
fed into the chamber (ventilation). Ranges of oxygen volume concentration below 20,95 % of oxygen can be
studied. The apparatus is not intended to control enriched oxygen conditions above atmospheric 20,95 %
oxygen concentration.
The measurement system prescribed in this document is based on the cone calorimeter apparatus described
in ISO 5660-1. Therefore, this document is intended to be used in conjunction with ISO 5660-1.
vi
FINAL DRAFT International Standard ISO/FDIS 5660-5:2026(en)

Reaction-to-fire tests — Heat release, smoke production and mass loss
rate —
Part 5:
Heat release rate (cone calorimeter method) and smoke production
rate (dynamic measurement) under reduced oxygen atmospheres
1 Scope
This document specifies the apparatus and procedure for measuring reaction to fire behaviour under reduced
oxygen atmospheres. 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.
2 Normative references
ISO 5660-1:2015+A1:2019-1, Reaction-to-fire tests — Heat release, smoke production and mass loss rate —
Part 1: Heat release rate (cone calorimeter method) and smoke production rate (dynamic measurement))
ISO 13927:2023, Plastics — Simple heat release test using a conical radiant heater and a thermopile detector
ISO 13943, Fire safety — Vocabulary
23 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5660-1, ISO 13943 and the following
apply.
ISO and IEC maintain terminologicalterminology 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/
2.13.1 3.1
ambient atmosphere
atmosphere with an oxygen volume concentration of approximately 20,95 % in a control volume and
unrestricted air flow into the same control volume
2.23.2 3.2
reduced oxygen atmosphere
vitiated atmosphere with either one of the following conditionsor under-ventilated atmosphere that differ
from ambient atmospheres:
ISO/TS FDIS 5660-5:2020(E2026(en)
a) A vitiated atmosphere: is an atmosphere with less oxygen molecules than in ambient air in the same volume
at same temperature and pressure levels (oxygen concentration below 20,95 %; vitiated conditions), with the remaining
molecules balanced by inert gas molecules.
b) Note 1 to entry: An under-ventilated atmosphere: is an atmosphere with a limited air supply that leads to
fewer oxygen molecules per time supplied to a combustion reaction than needed to allow stoichiometric reactions to take
place (under-ventilated conditions)).
2.33.3 3.3
vitiation-controlled conditionscondition
conditionscondition under which the volume concentration of oxygen is intentionally controlled or reduced
in the combustion environment
Note 1 to entry: Vitiation-controlled conditions represent an oxygen depleted fire environment.
2.43.4 3.4
ventilation-controlled conditionscondition
conditionscondition in which the supply rate of (ambient or vitiated) air to the combustion environment is
intentionally controlled or limited
Note 1 to entry: Ventilation-controlled conditions represent a fire environment with limited fresh air supply.
34 Symbols
For the purposes of this document, the symbols given in ISO 5660-1 and the following apply.
Table 1 — Symbols and their designations and units
Symbol Designations Unit
𝐴 initially exposed surface area of the specimen m
𝑆
½ ½ ½ 1/2 1/2
𝐶 orifice flow meter calibration constant m g K m g
1/2
K
𝛾 thermal expansion factor (dimensionless)—
𝛾˜ thermal changeable dilution factor (dimensionless)—
−1
𝛥ℎ net heat of combustion kJ g
𝑐
−1
𝑚˙ mass flow rate in the exhaust duct during the test kg s
𝑒
−1
𝑚˙ initial mass flow rate in the exhaust duct kg s
𝑒
−1
𝑚˙ mass flow rate of fuel, burning rate of the specimen
kg s
𝑓
𝐸
−1
𝑚˙ mass flow rate of the incoming gas mixture to the enclosure kg s
𝑔
𝛥𝑝 orifice meter pressure differential Pa
𝑞˙ (𝑡) heat release rate kW
−2
𝑞˙ (𝑡) heat release rate per unit area kW m
𝐴
𝜙 oxygen depletion factor (dimensionless)—
𝑇 absolute temperature of gas at the orifice meter K
𝑒
˙
volume flow rate of Airair Ll/min
𝑉
𝐴
𝐸
˙
𝑉 volume flow rate of Gasgas to the enclosure
Ll/min
𝑔
˙
volume flow rate of Nitrogennitrogen gas
𝑉 Ll/min
𝑁
𝑋 oxygen concentration in air (bottled, pressurized) (dimensionless)—
O , 𝐴𝑖𝑟
value of combustion gas oxygen analyser reading, before delay time
𝑋
𝑂
(dimensionless)—
correction
A
actual value of combustion gas oxygen analyser reading
𝑋 (dimensionless)—
𝑂
𝐴
initial baseline valueaverage of combustion gasthe oxygen analyser
𝑋
𝑂
reading (with
(dimensionless)—
enclosure environment established)output measured during the 1-min
initial baseline measurement
𝑆
𝐴
surrounding baseline valueaverage of the oxygen analyser reading
𝑋
𝑂
(output measured during the 1-min surroundings baseline
(dimensionless)—
measurements before the enclosure environment established –
enclosure door open)has been supplied with air or gas
𝐴
𝑋 actual value of combustion gas carbon monoxide analyser reading (dimensionless)—
𝐶𝑂
𝐴
actual value of combustion gas carbon dioxide analyser reading
𝑋 (dimensionless)—
𝐶𝑂
𝐸
oxygen concentration in the enclosure
𝑋 (dimensionless)—
𝑂
𝑆
𝐴
surrounding baseline value of combustion gas carbon dioxide analyser
𝑋
𝐶𝑂
reading (before enclosure environment established – enclosure door (dimensionless)—
open)
𝑆
Surroundingsurrounding value of water vaporvapour
𝑋 (dimensionless)—
𝐻 𝑂
H relative air humidity of the surrounding before the test %
Pp ambient pressure, in Pa, of the surrounding before the test Pa
T is the ambient temperature, in K, of the surrounding before the test K
a
45 Principle
The principle of this test method is based on the observation that, generally, both thermal and chemical
products of a combustion reaction vary in quantity and quality depending on the atmospheric environmental
conditions in which the reactions occurs. This test method provides a controlled environment to assess the
contribution that a product under test can make to the rate of heat release, the production rate of gaseous
products, and the smoke production rate, in either different reduced oxygen atmospheres and/or differently
ventilated atmospheres, or both, during the product’s involvement in fire. The properties are determined on
small representative specimens. Specimens in the test are burned in ambient atmospheres or predetermined
reduced oxygen atmospheres, while being subjected to a predetermined external irradiance within the range
−2 −2
of 0 kW m to 50 kW m . Measurements are made of oxygen and other gas concentrations in the exhaust,
light transmission, exhaust gas flow rates, and specimen mass.
Heat release rate measurement is based on the observation that the net heat of combustion is proportional to
the amount of oxygen required for combustion. The relationship is that approximately 13,1 × 10 kJ of heat
are released per kilogram of oxygen consumed. This is accurate within ± ± 5 % for complete combustion and
ISO/TS FDIS 5660-5:2020(E2026(en)
differs by ±20 % considerably for incomplete combustion. Measurements of oxygen concentrations and total
exhaust gas flow rates are conventionally made. Enhanced measurements of carbon dioxide concentrations,
carbon monoxide concentrations, other species concentrations, soot, water vapor,vapour and unburnt fuel
allow application of appropriate corrections depending on stoichiometries of the combustion reactions. These
measurements are used to calculate the mass of oxygen consumed. Results are reported as heat release rate
and total heat release, both normalized to exposed specimen surface area. The heat release rate of a burning
specimen is calculated as the product of the oxygen mass consumed by the fire and the averaged
3 −1
proportionality 13,1 × 10 kJ kg with corrections for incomplete combustion. The enhanced measurements
for carbon dioxide, carbon monoxide, and water vaporvapour are applied for general corrections in this
document. Where available, specific values for the proportionality can be used as quotient of the heat of
combustion of a burning fuel and its stochiometric oxygen to fuel mass ratio. The total heat release is
calculated by numerical integration of the heat release rate over the time interval being considered. Both
variables are normalized to area because heat release is proportional to the burning surface area.
The principle of the smoke measurement is based on the observation that, generally, the intensity of light that
is transmitted through a volume of combustion products is an exponentially decreasing function of distance.
Measurements are made of exhaust gas obscuration, exhaust gas flow rate, and mass loss rate of the specimen.
Exhaust gas obscuration is measured as the fraction of laser light intensity that is transmitted through the
mixture of gases, aerosols, and particles in the exhaust duct. This fraction is used to calculate the extinction
coefficient according to Bouguer’s law. In particular, with non-flaming and anaerobic pyrolysis processes,
extinction coefficients differ from extinction values for combustion smoke. The test results are reported in
terms of smoke production and smoke production rate, both normalized to exposed specimen surface area.
Smoke production rate is calculated as the product of the extinction coefficient and the volumetric flow rate
of the smoke in the exhaust duct. Smoke production is calculated by numerical integration of the smoke
production rate over the time interval being considered. The variables reported are normalized to area
because smoke production is proportional to area.
Gas production measurements are performed by measuring gas concentrations in the exhaust duct. Gas
production rates are calculated from those concentration measurements utilizing general equationsformulae
and relations. Species yields are derived from the specific gas mass flow rate divided by the actual fuel mass
loss rate at the same time interval.
Atmospheric environmental conditions may range from approximately 1 % to 20,95 % of oxygen and
150 Ll/min to 180 Ll/min volume flow rate (when ventilation-controlled conditions are not intended). They
are predetermined and controlled within the combustion environment by maintaining the ratio and volume
flow rate of air and nitrogen gas respectively. The oxygen concentration in the atmospheric conditions and the
total gas flow rate to the environment are monitored with relevant measurement devices. Air and nitrogen
gas shall be provided either as bottled gases or as oil-free pressurized air from a compressor, and liquid
nitrogen vaporizer respectively.
56 Apparatus
6.1 General
The apparatus described in this document allows measurement of reaction to fire behaviour under reduced
oxygen atmospheres. Ranges of oxygen volume concentration below 20,95 % of oxygen can be studied. For
those conditions above 15 % of oxygen, flaming combustion is usually expected. For those below 15 % of
oxygen, flaming maycan occur but is generally not expected to occur for many products. Anaerobic pyrolysis
experiments at close to 0 % of oxygen can be carried out in absence of the oxygen depletion measurements.
The apparatus utilizes the components and controls of the apparatus specified in ISO 5660-1 supplemented
by apparatus modification detailed in this document to facilitate testing under reduced oxygen atmospheres.
This principally consists of replacing the standard cone heater assembly by a second unit housed in a chamber
that can by supplied with metered mixtures of air and nitrogen. Measurements are otherwise similar to those
made in ISO 5660-1.
The gas measurement equipment detailed in ISO 5660-1:2015+A1:2019, shall be used
An apparatus exclusively for anaerobic pyrolysis experiments may alternatively utilize components and
controls of the apparatus specified in ISO 13927.
A schematic representation of the apparatus required for this document is given in Figure 1 Figure 1.
Components described in ISO 5660-1 are marked. Components specific to reduced oxygen atmosphere testing
are specified in 6.16.1 to 6.76.7 of this document.

Key
1 exhaust hood
2 exhaust duct
3 sampling ring
4 pressure ports
5 orifice plate
6 thermocouple
7 stack
8 exhaust fan
9 laser extinction beam
10 chimney
11 cone heater
ISO/TS FDIS 5660-5:2020(E2026(en)
12 radiation shield
13 ignition circuit
14 controlled-atmosphere chamber (enclosure)
15 sample holder and specimen
16 cooled shield
17 weighing device
18 baffles
19 mass flow meter
20 air
21 nitrogen
Figure 1 — Overview of the arrangement of enclosure, chimney and cone calorimeter according to
ISO 5660-1
5.1 General
The conical shaped radiant heater described in ISO 5660-1:2015+A1:2019 shall be integrated into the top face
of an enclosure. The cabinet shall also include the radiation shield, the weighing device with an additional
cooling shield, the specimen holder and the ignition circuit as described in ISO 5660-1:2015+A1:2019. The
heat flux meter and housing and the calibration burner shall also be provided. Appropriate mountings shall
be available to perform calibration measurements using the heat flux meter and calibration inside the
enclosure. A gas mixing and supply system shall be connected to the enclosure to allow adjusting the
atmospheric conditions.
5.26.2 Heater and enclosure and chimney arrangement with cone calorimeter as per
ISO 5660-1
6.2.1 General
The test enclosure described in 6.2.26.2.1 replaces the standard cone heater assembly in the ISO 5660-1
apparatus. It shall be centred underneath the exhaust hood and can be used in each of the following
configurations using a chimney on top of the enclosure as described in 6.46.4.
a) 1) When testing with an enclosure gas supply rate lower than the exhaust flow rate, the enclosure
and chimney should not be linked directly to the exhaust hood. Air from the surroundings shall be allowed
to enter the exhaust hood.
NOTE 1 The effect of the chimney in the unlinked configuration on various results are discussed in
Reference [2][2].
NOTE 2 An exhaust flow rate that exceeds the enclosure supply rate would cause under pressure, leakages, and
potentially uncontrolled conditions in the enclosure.
b) 2) When undertaking anaerobic pyrolysis experiments these can be carried out in either unlinked
(shown in 6.1Item 1)) or linked apparatus (Item 2) depending on the applicable gas supply rate or if the
enclosure is stand-alone without the oxygen depletion measurement equipment running.
Annex CAnnex C specifies more details about the stand-alone arrangement.
Regardless of the configuration or the enclosure inlet gas flow rate, the exhaust flow rate in the duct shall be
sufficiently high to reliably entrain all combustion/pyrolysis products released during the process. The
minimum exhaust flow rate at the beginning of the test shall be at least 0,012 ± 0,002 m /s.
5.2.16.2.2 Enclosure
A stainless steel enclosure as shown in Figure 2 Figure 2 shall have internal dimensions of W × D × H
of (370 ± 20) mm × (320 ± 20) mm × (330 ± 20) mm. A door shall be mounted on the front of the enclosure to
provide access to all inner parts and to allow specimen loading. When opened for specimen loading, a door
maycan allow significant amounts of air entering the enclosure. This maycan unintentionally change the
predetermined controlled atmosphere. An alternative opening scheme may be used if it allows only minimum
air entering the enclosure during specimen loading. At least one wall or door element shall contain a window
to allow the specimen to be observed during a test. At least one gas connection port shall be mounted at the
level of the sample that allows gas sampling of the enclosure atmosphere. Additional ports maycan be present
for cooling water entry, additional gas sampling , and/or temperature measurement, or all, as well as
extinguishing, and radiation measurement equipment.

a) Top view
b) Side view c) Front view
Key
1 radiant heater
2 enclosure
3 water-cooled collar
Figure 2 — Overview of the enclosure
ISO/TS FDIS 5660-5:2020(E2026(en)
All connections of wall assemblies, ports and openings shall be tightly sealed to prevent surrounding air from
penetrating in the enclosure during the test.
The conical heater, specified in ISO 5660-1:2015+A1:2019 shall be mounted in the centre of the top face of the
−2
enclosure. It shall be capable of producing an irradiance level on the surface of the specimen of 0 kW m to
−2
50 kW m . Higher heat flux levels maycan be possibleused if the equipment is suitable for high temperature
conditions. A water-cooled collar should be mounted between the heater and the top of the enclosure to
minimize warping of the top plate due to the hot electrical heater. Heat resistant sealing material shall be used
for sealing the cone heater openings against unintended air diffusion/ or penetration into the enclosure.
In accordance with applicable sectionsclauses of ISO 5660-‑1:2015+A1:2019, the enclosure shall contain a
radiation shield, an ignition circuit and a specimen holder. The enclosure shall be capable of incorporating and
operating the weighing device. The weighing device may be located outside the enclosure if proper sealing of
the connection rod is ensured and accurate sample mass measurement is provided.
Two local entry points or a mesh of points shall be provided in the base of the enclosure to feed the enclosure
with a pre-mixed mixture of air and gases in a suitable ratio to create the desired test atmosphere. The entry
points shall be designed in a way that minimizes high local flow rates inside the enclosure. A baffle design that
has been used to meet these requirements is shown in Figure 3 Figure 3. Alternative equipment, such as
screens and beads, or similar may be used if it minimizes high local flow rates. Screens and beads at the bottom
of the enclosure are expected to provide uniformly consistent and upward inlet flow velocity. Baffles as per
Figure 3 Figure 3 shall be used. When using an alternative to the baffles in Figure 3 Figure 3,, comparative
tests between an ISO 5660-‑1:2015+A1:2019 apparatus and the apparatus described in this document shall
be conducted for the same product at 20,95 % of oxygen. Time to ignition and heat release rate measurement
results shall be compared.
Key
1 baffles
Figure 3 — Baffles at base of chamber
5.36.3 Water-cooling for weighing device
A water-cooled shield or housing shall be provided on top or around the weighing device to ensure proper
weight measurement while protecting the weighing device from the heat inside the enclosure during a test.
The device’s connection rod may be cooled as well. However, water-cooling shall not affect the specimen mass
measurement at any time before or during a test. Weighing devices that are located outside the enclosure do
not require water-cooling.
5.46.4 Chimney
A circular cross-section chimney shall be mounted on top of the top-plate of the conical heater. The axis of the
chimney shall coincide with the axis of the heater. The chimney shall have a length of (600 ± 2) mm and an
internal diameter of (115 ± 2) mm following the chimney design i
...