SIST EN IEC 60695-6-1:2021

SLOVENSKI STANDARD
01-november-2021
Nadomešča:
SIST EN 60695-6-1:2005
SIST EN 60695-6-1:2005/A1:2010
Preskušanje požarne ogroženosti - 6-1. del: Otemnitev dima - Splošna navodila
(IEC 60695-6-1:2021)
Fire hazard testing - Part 6-1: Smoke obscuration - General guidance (IEC 60695-6-
1:2021)
Prüfungen zur Beurteilung der Brandgefahr - Teil 6-1: Sichtminderung durch Racuh -
Allgemeiner Leitfaden (IEC 60695-6-1:2021)
Essais relatifs aux risques du feu - Partie 6-1: Obscurcissement dû à la fumée -
Recommandations générales (IEC 60695-6-1:2021)
Ta slovenski standard je istoveten z: EN IEC 60695-6-1:2021
ICS:
13.220.40 Sposobnost vžiga in Ignitability and burning
obnašanje materialov in behaviour of materials and
proizvodov pri gorenju products
29.020 Elektrotehnika na splošno Electrical engineering in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60695-6-1

NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2021
ICS 13.220.99; 29.020 Supersedes EN 60695-6-1:2005 and all of its
amendments and corrigenda (if any)
English Version
Fire hazard testing - Part 6-1: Smoke obscuration - General
guidance
(IEC 60695-6-1:2021)
Essais relatifs aux risques du feu - Partie 6-1: Prüfungen zur Beurteilung der Brandgefahr - Teil 6-1:
Obscurcissement dû à la fumée - Recommandations Sichtminderung durch Racuh - Allgemeiner Leitfaden
générales (IEC 60695-6-1:2021)
(IEC 60695-6-1:2021)
This European Standard was approved by CENELEC on 2021-09-09. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60695-6-1:2021 E

European foreword
The text of document 89/1472/CDV, future edition 3 of IEC 60695-6-1, prepared by IEC/TC 89 “Fire
hazard testing” was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2022-06-09
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2024-09-09
document have to be withdrawn
This document supersedes EN 60695-6-1:2005 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60695-6-1:2021 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 60695-1-12 NOTE Harmonized as EN IEC 60695-1-12
ISO 5659-2 NOTE Harmonized as EN ISO 5659-2
IEC 61034-1 NOTE Harmonized as EN 61034-1
IEC 61034-2 NOTE Harmonized as EN 61034-2
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
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.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60695-1-10 - Fire hazard testing - Part 1–10: Guidance EN 60695-1-10 -
for assessing the fire hazard of
electrotechnical products - General
guidelines
IEC 60695-1-11 - Fire hazard testing - Part 1–11: Guidance EN 60695-1-11 -
for assessing the fire hazard of
electrotechnical products - Fire hazard
assessment
IEC 60695-4 - Fire hazard testing - Part 4: Terminology EN IEC 60695-4 -
concerning fire tests for electrotechnical
products
IEC 60695-6-2 - Fire hazard testing - Part 6–2: Smoke EN IEC 60695-6-2 -
obscuration - Summary and relevance of
test methods
IEC Guide 104 - The preparation of safety publications and - -
the use of basic safety publications and
group safety publications
ISO 13943 2017 Fire safety - Vocabulary EN ISO 13943 2017
ISO/IEC Guide 51 - Safety aspects - Guidelines for their - -
inclusion in standards
IEC 60695-6-1 ®
Edition 3.0 2021-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
HORIZONTAL PUBLICATION
PUBLICATION HORIZONTALE
Fire hazard testing –
Part 6-1: Smoke obscuration – General guidance

Essais relatifs aux risques du feu –

Partie 6-1: Obscurcissement dû à la fumée – Recommandations générales

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 13.220.99; 29.020 ISBN 978-2-8322-1004-7

– 2 – IEC 60695-6-1:2021 © IEC 2021
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references. 7
3 Terms, definitions and symbols . 8
3.1 Terms and definitions . 8
3.2 Symbols . 10
4 General aspects of smoke test methods . 11
4.1 Fire scenarios and physical fire models . 11
4.2 Factors affecting smoke production . 12
4.2.1 General . 12
4.2.2 Modes of decomposition . 12
4.2.3 Ventilation and the burning environment . 16
4.2.4 Time and temperature . 16
4.2.5 Removal mechanisms for smoke particles. 16
5 Principles of smoke measurement . 16
5.1 General . 16
5.2 Bouguer's law . 16
5.3 Extinction area . 17
5.4 Log units . 18
5.5 Light sources . 18
5.6 Specific extinction area of smoke. 18
5.7 Mass optical density of smoke . 19
5.8 Visibility . 20
6 Static and dynamic methods . 20
6.1 Static methods . 20
6.1.1 Principles . 20
6.1.2 Extinction area of smoke . 20
6.1.3 Specific optical density of smoke . 21
6.1.4 Prediction of visibility . 21
6.2 Dynamic methods . 21
6.2.1 Principles . 21
6.2.2 Smoke production rate . 21
6.2.3 Total smoke production . 22
6.2.4 SMOGRA index . 22
7 Test methods . 23
7.1 Consideration of test methods . 23
7.2 Selection of test specimen . 24
8 Presentation of data . 24
9 Relevance of data to hazard assessment . 24
Annex A (informative) Calculation of visibility . 27
A.1 General . 27
A.2 Example. 27
Annex B (informative) Relationships between D and some other smoke parameters
s
as measured in ISO 5659-2 [4] . 29

IEC 60695-6-1:2021 © IEC 2021 – 3 –
Annex C (informative) Relationships between per cent transmission, as measured in a
"three metre cube" enclosure, and extinction area . 31
Bibliography . 33

Figure 1 – Different phases in the development of a fire within a compartment . 12
Figure 2 – Attenuation of light by smoke . 17
Figure 3 – Extinction area . 18
Figure 4 – Dynamic smoke measurement . 21
Figure 5 – Example SPRav versus t curve . 23
Figure 6 – SMOGRA curve derived from Figure 5 . 23
Figure 7 – Evaluation and consideration of smoke test methods . 26
Figure A.1 – Visibility (ω) versus extinction coefficient (k) . 27
Figure B.1 – Smoke parameters related to D as measured in ISO 5659-2 . 30
s
Figure C.1 – Extinction area (amount of smoke) related to per cent transmission as
measured in the "three metre cube" . 32

Table 1 – Characteristics of fire stages (from Table 1 in ISO 19706:2011) . 14
Table B.1 – Conversion from D to some other smoke parameters as measured in
s
ISO 5659-2 . 29
Table C.1 – Conversions from per cent transmission, as measured in the "three metre
cube" to amount of smoke (extinction area) . 31

– 4 – IEC 60695-6-1:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE HAZARD TESTING –
Part 6-1: Smoke obscuration –
General guidance
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as "IEC
Publication(s)"). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60695-6-1 has been prepared by IEC technical committee 89: Fire
hazard testing.
This third edition cancels and replaces the second edition of IEC 60695-6-1 published in 2005
and Amendment 1:2010. It constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– References to IEC TS 60695-6-30 (withdrawn in 2016) have been removed.
– References to IEC TS 60695-6-31 (withdrawn in 2016) have been removed.
– References to ISO 5659-2 have been inserted.
– The scope contains some additional text.
– Terms and definitions have been updated.

IEC 60695-6-1:2021 © IEC 2021 – 5 –
– Subclause 3.2 has been updated.
– Subclause 7.1 has been updated.
The text of this International Standard is based on the following documents:
Draft Report on voting
89/1472/CDV 89/1504/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
It has the status of a basic safety publication in accordance with IEC Guide 104 and
ISO/IEC Guide 51.
This International Standard is to be used in conjunction with IEC 60695-6-2.
In this standard, the following print types are used:
• italic font: terms defined in Clause 3.
A list of all parts in the IEC 60695 series, published under the general title Fire hazard testing,
can be found on the IEC website.
IEC 60695-6 consists of the following parts:
Part 6-1: Smoke obscuration – General guidance
Part 6-2: Smoke obscuration – Summary and relevance of test methods
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60695-6-1:2021 © IEC 2021
INTRODUCTION
In the design of an electrotechnical product the risk of fire and the potential hazards
associated with fire need to be considered. In this respect the objective of component, circuit
and equipment design, as well as the choice of materials, is to reduce the risk of fire to a
tolerable level even in the event of reasonably foreseeable (mis)use, malfunction or failure.
IEC 60695-1-10, IEC 60695-1-11, and IEC 60695-1-12 [1] provide guidance on how this is to
be accomplished.
Fires involving electrotechnical products can also be initiated from external non-electrical
sources. Considerations of this nature are dealt with in an overall fire hazard assessment.
The aim of the IEC 60695 series is to save lives and property by reducing the number of fires
or reducing the consequences of the fire. This can be accomplished by:
– trying to prevent ignition caused by an electrically energised component part and, in the
event of ignition, to confine any resulting fire within the bounds of the enclosure of the
electrotechnical product.
– trying to minimise flame spread beyond the product's enclosure and to minimise the
harmful effects of fire effluents including heat, smoke, and toxic or corrosive combustion
products.
One of the contributing hazards is the release of smoke, which may cause loss of vision
and/or disorientation which could impede escape from the building or fire fighting.
Smoke particles reduce the visibility due to light absorption and scattering. Consequently,
people may experience difficulties in finding exit signs, doors and windows. Visibility is often
determined as the distance at which an object is no longer visible. It depends on many
factors, but close relationships have been established between visibility and the
measurements of the extinction coefficient of smoke – see Annex A.
The production of smoke and its optical properties can be measured as well as other fire
properties, such as heat release, flame spread, and the production of toxic gas and corrosive
effluent. This document serves as a guidance document and focuses on obscuration of light
by smoke.
___________
Numbers in square brackets refer to the bibliography.

IEC 60695-6-1:2021 © IEC 2021 – 7 –
FIRE HAZARD TESTING –
Part 6-1: Smoke obscuration –
General guidance
1 Scope
This part of IEC 60695 gives guidance on:
a) the optical measurement of obscuration of smoke;
b) general aspects of optical smoke test methods;
c) consideration of test methods;
d) expression of smoke test data;
e) the relevance of optical smoke data to hazard assessment.
This basic safety publication focusing on safety guidance is primarily intended for use by
technical committees in the preparation of safety publications in accordance with the
principles laid down in IEC Guide 104 and ISO/IEC Guide 51.
One of the responsibilities of a technical committee is, wherever applicable, to make use of
basic safety publications in the preparation of its publications.
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.
IEC 60695-1-10, Fire hazard testing – Part 1-10: Guidance for assessing the fire hazard of
electrotechnical products – General guidelines
IEC 60695-1-11, Fire hazard testing – Part 1-11: Guidance for assessing the fire hazard of
electrotechnical products – Fire hazard assessment
IEC 60695-4, Fire hazard testing – Part 4: Terminology concerning fire tests for
electrotechnical products
IEC 60695-6-2, Fire hazard testing – Part 6-2: Smoke obscuration – Summary and relevance
of test methods
IEC Guide 104, The preparation of safety publications and the use of basic safety publications
and group safety publications
ISO/IEC Guide 51, Safety aspects – Guidelines for their inclusion in standards
ISO 13943:2017, Fire safety – Vocabulary

– 8 – IEC 60695-6-1:2021 © IEC 2021
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943:2017 and
IEC 60695-4, some of which are reproduced below, apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
extinction area of smoke
product of the volume occupied by smoke (3.1.10) and the extinction coefficient (3.1.2) of the
smoke
Note 1 to entry: The extinction area of smoke is a measure of the amount of smoke. The typical unit is m .
[SOURCE: ISO 13943:2017, 3.110]
3.1.2
extinction coefficient
natural logarithm of the ratio of incident light intensity to transmitted light intensity, per unit
light path length
-1
Note 1 to entry: The typical unit is m .
[SOURCE: ISO 13943:2017, 3.111]
3.1.3
mass optical density of smoke
optical density of smoke (3.1.6) multiplied by a factor which is the volume of the test chamber
divided by the product of the mass lost from the test specimen and the light path length
2 −1
Note 1 to entry: The typical unit is m⋅g .
Note 2 to entry: Optical density of smoke = V/(Δm L), where V is test chamber volume, Δm is test specimen mass
loss and L is light path length.
[SOURCE: ISO 13943:2017, 3.265]
3.1.4
obscuration of smoke
reduction in the intensity of light due to its passage through smoke (3.1.10)
Note 1 to entry: Compare with the terms extinction area of smoke (3.1.1), extinction coefficient (3.1.2), opacity of
smoke (3.1.5), optical density of smoke (3.1.6), smoke obscuration (3.1.11), specific extinction area of
smoke (3.1.13) and specific optical density of smoke (3.1.14).
Note 2 to entry: In practice, obscuration of smoke is usually measured as the transmittance which is normally
expressed as a percentage.
Note 3 to entry: The obscuration of smoke causes a reduction in visibility (3.1.6).
[SOURCE: ISO 13943:2017, 3.286]

IEC 60695-6-1:2021 © IEC 2021 – 9 –
3.1.5
opacity of smoke
ratio of incident light intensity to transmitted light intensity through smoke (3.1.10), under
specified conditions
Note 1 to entry: Also, obscuration of smoke (3.1.4), smoke obscuration (3.1.11).
Note 2 to entry: The opacity of smoke is the reciprocal of transmittance.
Note 3 to entry: The opacity of smoke is dimensionless.
[SOURCE: ISO 13943:2017, 3.287]
3.1.6
optical density of smoke
measure of the attenuation of a light beam passing through smoke (3.1.10) expressed as the
logarithm to the base 10 of the opacity of smoke (3.1.5)
Note 1 to entry: Compare with the term specific optical density of smoke (3.1.14).
Note 2 to entry: The optical density of smoke is dimensionless.
[SOURCE: ISO 13943:2017, 3.288]
3.1.7
physical fire model
laboratory process, including the apparatus, the environment and the fire test procedure
intended to represent a certain phase of a fire
[SOURCE: ISO 13943:2017, 3.298]
3.1.8
SMOGRA
smoke growth rate parameter that is a function of the rate of smoke production and the time of
smoke production
Note 1 to entry: Further details are given in 6.2.4.
3.1.9
SMOGRA index
maximum value of SMOGRA (3.1.8) during a defined test period
Note 1 to entry: Further details are given in 6.2.4.
3.1.10
smoke
visible part of a fire effluent
[SOURCE: ISO 13943:2017, 3.347]
3.1.11
smoke obscuration
reduction of light transmission by smoke (3.1.10), as measured by light attenuation
Note 1 to entry: Compare with the terms extinction area of smoke (3.1.1), extinction coefficient (3.1.2),
obscuration of smoke (3.1.4), opacity of smoke (3.1.5), optical density of smoke (3.1.6), specific extinction area of
smoke (3.1.13) and specific optical density of smoke (3.1.14).
[SOURCE: ISO 13943:2017, 3.349]

– 10 – IEC 60695-6-1:2021 © IEC 2021
3.1.12
smoke production rate
amount of smoke (3.1.10) produced per unit time in a fire or fire test
Note 1 to entry: The smoke production rate is calculated as the product of the volumetric flow rate of smoke
(3.1.10) and the extinction coefficient (3.1.2) of the smoke at the point of measurement.
2 −1
Note 2 to entry: The typical unit is m⋅s .
[SOURCE: ISO 13943:2017, 3.351]
3.1.13
specific extinction area of smoke
extinction area of smoke (3.1.1) produced by a test specimen in a given time period divided
by the mass lost from the test specimen in the same time period
2 −1
Note 1 to entry: The typical unit is m⋅g .
[SOURCE: ISO 13943:2017, 3.358]
3.1.14
specific optical density of smoke
optical density of smoke (3.1.6) multiplied by a geometric factor
Note 1 to entry: The geometric factor is V/(A·L), where V is the volume of the test chamber, A is the area of the
exposed surface of the test specimen, and L is the light path length.
Note 2 to entry: The use of the term "specific" does not denote "per unit mass" but rather denotes a quantity
associated with a particular test apparatus and area of the exposed surface of the test specimen.
Note 3 to entry: The specific optical density of smoke is dimensionless.
[SOURCE: ISO 13943:2017, 3.360]
3.1.15
visibility
maximum distance at which an object of defined size, brightness and contrast can be seen
and recognized
[SOURCE: ISO 13943:2017, 3.420]
3.2 Symbols
Symbol Quantity Typical units
A exposed area of test specimen
m
linear decadic absorption coefficient
D 1
−
m
(commonly called optical density per metre)
D' optical density of smoke
dimensionless
2 1
D mass optical density of smoke −
mass
m kg
D
s specific optical density of smoke
dimensionless
D (also D )
max m
maximum specific optical density of smoke dimensionless
I
intensity of incident light cd
I/T opacity of smoke (ratio of incident light to transmitted light)
dimensionless
linear Napierian absorption coefficient
k 1
−
m
(commonly called extinction coefficient)
L
light path length through smoke m
∆m mass loss of test specimen
kg
ṁ −
mass loss rate
kg s
IEC 60695-6-1:2021 © IEC 2021 – 11 –
Symbol Quantity Typical units
S
extinction area of smoke (also total smoke) m
Ṡ smoke production rate
2 −1
m s
(rate of change of extinction area)
t
time s
∆t s
sampling time interval
T cd
intensity of transmitted light
V
volume of chamber m
V̇ 3 −1
m s
volume flow rate of smoke
2 −1
σ
f specific extinction area of smoke m kg
a constant of proportionality between visibility and extinction
γ
dimensionless
coefficient
ω m
visibility
NOTE 1 The quantities based on log , i.e. D, D′, D , D and D , have similar symbols but they are
10 max mass s
different quantities and have different units.
NOTE 2 The use of the term "specific" in the case of specific optical density of smoke, D , does not denote
s
"per unit mass".
4 General aspects of smoke test methods
4.1 Fire scenarios and physical fire models
During recent years, major advances have been made in the analysis of fire effluents. It is
recognized that the composition of the mixture of combustion products is particularly
dependent upon the nature of the combusting materials, the prevailing temperatures and
ventilation conditions, especially access of oxygen to the seat of the fire. Table 1 shows how
the different types of fire relate to the changing atmosphere. Conditions for use in laboratory
tests (small or large-scale) can be derived from the table in order to correspond, as far as
possible, to real-scale fires.
Fire involves a complex and interrelated array of physical and chemical phenomena. As a
result, it is difficult to simulate all aspects of a real-scale fire in a smaller scale apparatus.
This problem of physical fire model validity is perhaps the single most perplexing technical
problem associated with all fire testing.
General guidance for assessing the fire hazard of electrotechnical products is given in
IEC 60695-1-10 and IEC 60695-1-11.
After ignition, fire development may occur in different ways depending on the environmental
conditions, as well as on the physical arrangement of the combustible materials. However, a
general pattern can be established for fire development within a compartment, where the
general temperature-time curve shows three stages, plus a decay stage (see Figure 1).
Stage 1 is the incipient stage of the fire prior to sustained flaming, with little rise in the fire
room temperature. Ignition and smoke generation are the main hazards during this stage.
Stage 2 (developing fire) starts with ignition and ends with an exponential rise in the fire room
temperature. Spread of flame and heat release are the main hazards in addition to smoke
during this stage. Stage 3 (fully developed fire) starts when the surface of all of the
combustible contents of the room has decomposed to such an extent that sudden ignition
occurs all over the room, with a rapid and large increase in temperature (flash-over).

– 12 – IEC 60695-6-1:2021 © IEC 2021
At the end of stage 3, the combustibles and/or oxygen have been largely consumed and
hence the temperature decreases at a rate which depends on the ventilation and the heat and
mass transfer characteristics of the system. This is known as decay.
In each of these stages, a different mixture of decomposition products may be formed and
this, in turn, influences the smoke produced during that stage. In order to select an
appropriate fire test, information is required on the fire scenario being considered, in
particular the conditions of incident heat flux, oxygen availability and the facilities for venting
the smoke.
Figure 1 – Different phases in the development of a fire within a compartment
4.2 Factors affecting smoke production
4.2.1 General
Many factors affect the production of smoke and the properties of smoke. A full description of
such properties is not possible, but the influence of several important variables is recognized.
4.2.2 Modes of decomposition
Smoke is a consequence of combustion. Combustion may be flaming or non-flaming, including
smouldering, and these different modes of combustion may produce quite different types of
smoke. In non-flaming combustion, volatiles are evolved at elevated temperatures. When they
mix with cool air, they condense to form spherical droplets which appear as a light-coloured
smoke aerosol.
Flaming combustion produces a black carbon-rich smoke in which the particles have a very
irregular shape. The smoke particles from flaming combustion are formed in the gas phase
and in regions where oxygen concentrations are low enough to cause incomplete combustion.
The carbonaceous smoke particles in the flames emit radiant energy (as black-body emission)
which is seen as yellow luminosity.
The particle size of the spherical droplets from non-flaming combustion is generally of the
order of 1 µm, whereas the size of the irregular soot particles from flaming combustion is
often larger but much harder to determine and is dependent on the measuring technique.
It is often observed for wood fires that the amount of smoke is less with flaming combustion
than with non-flaming combustion. For plastics, however, no such generalization can be
made: the smoke produced under non-flaming conditions can be less or more than under
flaming conditions. For these reasons, it is important to record in a smoke test whether
ignition occurs, as well as the times of ignition and extinction of flames on the test specimen.

IEC 60695-6-1:2021 © IEC 2021 – 13 –
In addition, cold smoke may be generated from the rear of composites; this may differ
substantially in colour and composition from the smoke produced from the exposed surface.

– 14 – IEC 60695-6-1:2021 © IEC 2021
Table 1 – Characteristics of fire stages (from Table 1 in ISO 19706:2011)
Heat flux to Max. temperature Oxygen volume
[CO]
100×[CO2]
Fuel/air
fuel surface
°C % [CO2]
Fire stage equivalence
([CO2]+ [CO])
ratio (plume)
% efficiency
kW/m2 Fuel surface Upper layer Entrained Exhausted v/v
1. Non-flaming
a. self-sustaining not
d
450 to 800 20 20 – 0,1 to 1 50 to 90
25 to 85
(smouldering) applicable
b. oxidative pyrolysis from
b c c
– 300 to 600 a 20 20 < 1
externally applied radiation
c. anaerobic pyrolysis from
b c c
– 100 to 500 0 0 >> 1
externally applied radiation
d e
2. Well-ventilated flaming 0 to 60 350 to 650 50 to 500 ≈ 20 ≈ 20 < 1 < 0,05 > 95
f
3. Underventilated flaming
a. small, localized fire,
a
generally in a poorly ventilated 0 to 30 50 to 500 15 to 20 5 to 10 > 1 0,2 to 0,4 70 to 80
300 to 600
compartment
g h i
b. post-flashover fire 50 to 150 350 to 650 > 600 < 15 < 5 > 1 0,1 to 0,4 70 to 90
___________
The Table 1 — Characteristics of fire stages taken from ISO 19706:2011, Guidelines for assessing the fire threat to people, is reproduced with the permission of the International
Organization for Standardization, ISO. This standard can be obtained from any ISO member and from the website of the ISO Central Secretariat at the following address:
www.iso.org. Copyright remains with ISO.

IEC 60695-6-1:2021 © IEC 2021 – 15 –
a
The upper limit is lower than for well-ventilated flaming combustion of a given combustible.
b
The temperature in the upper layer of the fire room is most likely determined by the source of the externally applied radiation and room geometry.
c
There are few data, but for pyrolysis this ratio is expected to vary widely depending on the material chemistry and the local ventilation and thermal conditions.
d
The fire's oxygen consumption is small compared to that in the room or the inflow, the flame tip is below the hot gas upper layer or the upper layer is not yet significantly
vitiated to increase the CO yield significantly, the flames are not truncated by contact with another object, and the burning rate is controlled by the availability of fuel.
e
The ratio can be up to an order of magnitude higher for materials that are fire-resistant. There is no significant increase in this ratio for equivalence ratios up to ≈ 0,75.
Between ≈ 0,75 and 1, some increase in this ratio may occur.
f
The fire's oxygen demand is limited by the ventilation opening(s); the flames extend into the upper layer.
g
Assumed to be similar to well-ventilated flaming.
h
The plume equivalence ratio has not been measured; the use of a global equivalence ratio is inappropriate.
i
Instances of lower ratios have been measured. Generally, these result from secondary combustion outside the room vent.

– 16 – IEC 60695-6-1:2021 © IEC 2021
The heat flux on the test specimen influences how the material burns; it is good practice to
evaluate the smoke generated from materials at low levels of incident irradiance (e.g.
-2 -2 -2 -2
15 kW⋅m to 25 kW⋅m ) as well as at higher levels (e.g. 40 kW⋅m to 50 kW⋅m ). In this way,
the effects of the growth phases of a fire on the smoke-generating propensity of a material
can be assessed.
4.2.3 Ventilation and the burning environment
Smoke production depends upon the fire scenario and not just on what material is being
burnt. It is known that, for some materials, the production of smoke is increased considerably
by restricted ventilation.
The rate of burning and the area involved in burning should always be considered when
determining smoke production in fires. A material generating small quantities of smoke per
element of burning area may give large quantities of smoke in a fire due to the rapid spread of
flames over large surface areas.
4.2.4 Time and temperature
The particle size distribution of smoke aerosols changes with time; smoke particles coagulate
as they age. Some properties also change with temperature so that the properties of aged, or
cold smoke may be different from young, hot smoke. These factors are important for fire
engineers when they are considering potential smoke movement in large buildings. These
factors also have to be considered when designing smoke tests.
NOTE Guidance on fire safety engineering is given in IEC 60695-1-12 [1].
4.2.5 Removal mechanisms for smoke particles
Large smoke particles may be removed by a number of mechanisms. In cumulative test
procedures where a radiant heat source is immersed in the combustion gases, reheated
decomposition may occur as the smoke particles recirculate. Other mechanisms for removal
of larger particles include the deposition of particles on the internal surfaces of the chamber
and the action of fan stirrers. Aspects of these mechanisms also occur in real fires when
smoke circulates within a fire compartment. Because these effects are possible in cumulative
smoke tests, it is recognized that the early stages of the exposure (for example the first
10 min) are the most relevant for the determination of the rate of smoke generation.
5 Principles of smoke measurement
5.1 General
Smoke consists of an aerosol of particles. It can either be measured as a function of its
gravimetric properties (the mass of smoke particles), its light-obscuring properties, or a
mixture of the two [3]. This document is concerned with the reduction of visibility caused by
the obscuration of smoke and therefore gravimetric methods are not discussed. Obscuring
properties are a function of the number, size and nature of the particles in the light path. If the
particles are considered as opaque, the capacity of the smoke to obscure light is related to
the sum of the cross-sectional areas of the particles in the light path. It is measured in units of
area, e.g. square metres (m ).
The measurements may be made in small-, large-, or real-scale tests. They may be performed
in closed systems which are called cumulative or static methods. They may also be performed
in flow-through systems, and these are called dynamic methods.
5.2 Bouguer's law
Optical smoke measurements are derived from Bouguer's law which describes the attenuation
of monochromatic light by an absorbing medium:

IEC 60695-6-1:2021 © IEC 2021 – 17 –
kL
I/T = e (1)
k = (1/L) ln(I/T) (2)
−1
(The units of k are reciprocal length, e.g. m )
where
T is the intensity of transmitted light;
I is the intensity of incident light;

L is the light path length through the smoke;
k is the linear Napierian absorption coefficient (extinction coefficie
...