IEC TS 60695-1-20:2008

IEC/TS 60695-1-20
Edition 1.0 2008-02
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Fire hazard testing –
Part 1-20: Guidance for assessing the fire hazard of electrotechnical products –
Ignitability – General guidance

Essais relatifs aux risques du feu –
Partie 1-20: Lignes directrices pour l'évaluation des risques du feu des produits
électrotechniques – Allumabilité – Lignes directrices générales

IEC/TS 60695-1-20:2008
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IEC/TS 60695-1-20
Edition 1.0 2008-02
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
BASIC SAFETY PUBLICATION
PUBLICATION FONDAMENTALE DE SÉCURITÉ
Fire hazard testing –
Part 1-20: Guidance for assessing the fire hazard of electrotechnical products –
Ignitability – General guidance

Essais relatifs aux risques du feu –
Partie 1-20: Lignes directrices pour l'évaluation des risques du feu des produits
électrotechniques – Allumabilité – Lignes directrices générales

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
R
CODE PRIX
ICS 13.220.40; 29.020 ISBN 2-8318-9602-9

– 2 – TS 60695-1-20 © IEC:2008
CONTENTS
FOREWORD.3
INTRODUCTION.5

1 Scope.6
2 Normative references .6
3 Terms and definitions .7
4 Principles of ignitability.10
4.1 Gases .10
4.1.1 Flammability limits .10
4.1.2 Arc fires.10
4.2 Liquids .10
4.2.1 Introduction .10
4.2.2 Ignition parameters.10
4.2.3 Insulating liquids.11
4.3 Solids.11
4.3.1 Introduction .11
4.3.2 Parameters affecting ignition .11
4.3.3 Metals .12
4.3.4 Carbon (graphite) and carbonaceous char .12
4.3.5 Reactive substances.13
4.3.6 Dust clouds .13
5 Consideration for the selection of test methods .13
5.1 Introduction .13
5.2 Fire scenario .13
5.3 Ignition sources.13
5.3.1 Internal sources.14
5.3.2 External sources.14
5.3.3 Arc ignition of materials .15
5.4 Types of test specimen.16
5.5 Test procedure and apparatus.16
6 Use and interpretation of results.17

Annex A (informative) Examples of accidents due to arc fires in underground
hydroelectric power plants or urban substations.18

Bibliography.19

TS 60695-1-20 © IEC:2008 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIRE HAZARD TESTING –
Part 1-20: Guidance for assessing the fire
hazard of electrotechnical products –
Ignitability – 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
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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
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6) All users should ensure that they have the latest edition of this publication.
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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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 60695-1-20, which is a technical specification, has been prepared by IEC technical
committee 89: Fire hazard testing.
It has the status of a basic safety publication in accordance with IEC Guide 104 and ISO/IEC
Guide 51.
– 4 – TS 60695-1-20 © IEC:2008
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
89/807/DTS 89/827/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This technical specification is to be used in conjunction with IEC 60695-1-21 .
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60695 series, under the general title Fire hazard testing, can
be found on the IEC website.
Part 1 consists of the following parts:
Part 1-10 : Guidance for assessing the fire hazard of electrotechnical products –
General guidelines
Part 1-11 : Guidance for assessing the fire hazard of electrotechnical products –
Fire hazard assessment
Part 1-20: Guidance for assessing the fire hazard of electrotechnical products –
Ignitability – General guidance
Part 1-21: Guidance for assessing the fire hazard of electrotechnical products –
Ignitability – Summary and relevance of test methods
Part 1-30: Guidance for assessing the fire hazard of electrotechnical products –
Preselection testing procedures – General guidelines
Part 1-40: Guidance for assessing the fire hazard of electrotechnical products –
Insulating liquids
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
___________
Under consideration.
TS 60695-1-20 © IEC:2008 – 5 –
INTRODUCTION
Fires are responsible for creating hazards to life and property as a result of the generation of
heat (thermal hazard), and also as a result of the production of toxic effluent, corrosive
effluent and smoke (non-thermal hazard). Fires start with ignition and then can grow, leading
in some cases to flash-over and a fully developed fire. Ignition resistance is therefore one of
the most important parameters of a material to be considered in the assessment of fire
hazard. If there is no ignition there is no fire.
For most materials (other than metals and other elements), ignition occurs in the gas phase.
Ignition occurs when combustible vapour, mixed with air, reaches a high enough temperature
for exothermic oxidation reactions to rapidly propagate. The ease of ignition is a function of
the chemical nature of the vapour, the fuel/air ratio and the temperature.
In the case of liquids, the combustible vapour is produced by vaporization of the liquid, and
the vaporization process is dependent on the temperature and chemical composition of the
liquid.
In the case of solids, the combustible vapour is produced by pyrolysis when the temperature
of the solid is sufficiently high. The vaporization process is dependent on the temperature and
chemical composition of the solid, and also on the thickness, density, specific heat, and
thermal conductivity of the solid.
The ease of ignition of a test specimen depends on many variables. Factors that need to be
considered for the assessment of ignitability are:
a) the geometry of the test specimen, including thickness and the presence of edges, corners
or joints;
b) the surface orientation;
c) the rate and direction of air flow;
d) the nature and position of the ignition source;
e) the magnitude and position of any external heat flux; and
f) whether the combustible material is a solid or a liquid.
In the design of any 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 to acceptable levels the
potential risks of fire even in the event of foreseeable abnormal use, malfunction or failure.
IEC 60695-1-10 , together with its companion, IEC 60695-1-11 , provide guidance on how
this is to be accomplished.
The primary aims are to prevent ignition caused by an electrically energized component part,
and in the event of ignition, to confine any resulting fire within the bounds of the enclosure of
the electrotechnical product.
Secondary aims include the minimization of any flame spread beyond the product’s enclosure
and the minimization of harmful effects of fire effluents including heat, smoke, and toxic or
corrosive combustion products.
Fires involving electrotechnical products can also be initiated from external non-electrical
sources. Considerations of this nature are dealt with in the overall risk assessment.
This technical specification gives an overview of ignitability and its relevance to the fire
hazard of electrotechnical products.
___________
Under consideration.
– 6 – TS 60695-1-20 © IEC:2008
FIRE HAZARD TESTING –
Part 1-20: Guidance for assessing the fire
hazard of electrotechnical products –
Ignitability – General guidance

1 Scope
IEC 60695-1-20, which is a technical specification provides guidance on the ignitability of
electrotechnical products and the materials from which they are formed. It gives guidance on;
a) the principles of ignitability,
b) the selection of appropriate test methods, and
c) the use and interpretation of results.
This technical specification is intended for use by technical committees in preparation of
standards in accordance with the principles laid down 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. The requirements, test
methods or test conditions of this basic publication will not apply unless specifically referred
to or included in the relevant publications.
2 Normative references
The following referenced documents are indispensable for the application 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 60695-1-21, Fire hazard testing – Part 1-21: Guidance for assessing the fire hazard of
electrotechnical products – Ignitability – Summary and relevance of test methods
IEC 60695-2-11, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods –
Glow-wire flammability test method for end-products
IEC 60695-2-12, Fire hazard testing – Part 2-12: Glowing/hot-wire based test methods –
Glow-wire flammability test method for materials
IEC 60695-2-13, Fire hazard testing – Part 2-13: Glowing/hot-wire based test methods –
Glow-wire ignitability test method for materials
IEC 60695-4:2005, Fire hazard testing – Part 4: Terminology concerning fire tests in
electrotechnical equipment
IEC 60695-8-3, Fire hazard testing – Part 8-3: Heat release – Heat release of insulating
liquids used in electrotechnical products
___________
Under consideration.
To be published.
TS 60695-1-20 © IEC:2008 – 7 –
IEC 60695-11-5, Fire hazard testing – Part 11-5: Test flames – Needle-flame test method –
Apparatus, confirmatory test arrangement and guidance
IEC 60695-11-10, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical
flame test methods
IEC 60695-11-11 , Fire hazard testing – Part 11-11: Test flames – Determination of the
ignition characteristic heat flux from a flame source
IEC 60695-11-20, Fire hazard testing – Part 11-20: Test flames – 500 W flame test methods
IEC Guide 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications
EN 14522, Determination of the auto ignition temperature of gases and vapours
ISO/IEC Guide 51:1999, Safety aspects – Guidelines for their inclusion in standards
ISO/IEC 13943:2000, Fire safety – Vocabulary
ISO 871, Plastics – Determination of ignition temperature using a hot-air furnace
ISO 2592, Determination of flash and fire points. Cleveland open cup method
ISO 2719, Petroleum products and lubricants - Determination of flash point – Pensky-Martens
closed cup method
ISO 5657, Reaction to fire tests – Ignitability of building products using a radiant heat source
ISO 10840, Plastics – Guidance for the use of standard fire tests
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
auto ignition temperature
lowest temperature (of a hot surface) at which under specified test conditions an ignition of a
flammable gas or flammable vapour in mixture with air or air/inert gas occurs
[EN 14522, definition 3.1]
3.2
combustion
exothermic reaction of a substance with an oxidizer
NOTE Combustion generally emits effluent accompanied by flames and/or visible light.
[ISO/IEC 13943:2000, definition 23]
3.3
fire
a) a process of combustion characterized by the emission of heat and effluent accompanied
by smoke, and/or flame, and/or glowing;
b) rapid combustion spreading uncontrolled in time and space
[IEC 60695-4:2005, definition 3.19]
___________
Under consideration.
– 8 – TS 60695-1-20 © IEC:2008
3.4
fire hazard
〈cause of fire〉 physical object or condition with a potential for an undesirable consequence
from fire
3.5
fire point
minimum temperature at which a material ignites and continues to burn for a specified time
after a standardized small flame has been applied to its surface under specified conditions
NOTE 1 It is expressed in degrees Celsius.
NOTE 2 In some countries the term "fire point" has an additional meaning: a location where fire fighting
equipment is sited, which may also comprise a fire-alarm call point and fire instruction notices.
[ISO/IEC 13943:2000, definition 53]
3.6
fire retardant (noun)
a substance added or a treatment applied to a material in order to suppress, reduce or delay
the combustion of the material
[IEC 60695-4:2005, definition 3.31]
3.7
fire scenario
a detailed description of conditions, including environmental, of one or more of the stages
from before ignition to the completion of combustion in an actual fire at a specific location, or
in a full-scale simulation
[IEC 60695-4:2005, definition 3.32]
3.8
flame (noun)
zone of combustion in the gaseous phase, usually with emission of light
[ISO/IEC 13943:2000, definition 60]
3.9
flame retardant (noun)
substance added, or a treatment applied, to a material in order to suppress or delay the
appearance of a flame and/or reduce its propagation (spread) rate
NOTE The use of flame retardants does not necessarily suppress fire.
[ISO/IEC 13943:2000, definition 65]
3.10
flaming combustion
combustion in gaseous phase, usually with emission of light
[ISO/IEC 13943:2000, definition 72]
3.11
flash-ignition temperature (FIT)
the minimum temperature at which, under specified test conditions, sufficient flammable
gases are emitted to ignite momentarily on application of a pilot flame
[ISO 871, definition 3.1]
3.12
flash-over
the rapid transition to a state of total surface involvement in a fire of combustible materials
within an enclosure
[IEC 60695-4:2005, definition 3.42]

TS 60695-1-20 © IEC:2008 – 9 –
3.13
flash point
the minimum temperature to which a product must be heated for the vapours emitted to ignite
momentarily in the presence of flame, under specified test conditions
NOTE Expressed in ˚C.
[IEC 60695-4:2005, definition 3.43]
3.14
fully developed fire
state of total involvement of combustible materials in a fire
[ISO/IEC 13943:2000, definition 80]
3.15
glowing combustion
combustion of a material in the solid phase without flame but with the emission of light from
the combustion zone
[ISO/IEC 13943:2000, definition 84]
3.16
ignitability
measure of the ease with which an item can be ignited, under specified conditions
[ISO/IEC 13943:2000, definition 91]
3.17
ignition
initiation of combustion
NOTE The term "ignition" in French has a very different meaning [state of body combustion].
[ISO/IEC 13943:2000, definition 96]
3.18
ignition source
source of energy that initiates combustion
[ISO/IEC 13943:2000, definition 97]
3.19
ignition temperature (minimum)
the (minimum) temperature of a material or of an ignition source at which sustained
combustion can be initiated under specified test conditions, as defined in the test method
NOTE Ignition requires a sufficient volume of flammable gas and oxidant (air). Sustained combustion requires a
sufficient rate of production of flammable gas. The minimum ignition temperature implies thermal stressing to
infinite time. For practical purposes, the standard should define the minimum ignition temperature appropriately.
[IEC 60695-4:2005, definition 3.51]
3.20
lower flammability limit (LFL)
lowest concentration of a flammable substance in air within which a self-propagating flame
can occur
3.21
spontaneous-ignition temperature (SIT)
minimum temperature at which ignition is obtained by heating, under specified test conditions,
in the absence of any additional flame ignition source
[ISO 871, definition 3.2]
– 10 – TS 60695-1-20 © IEC:2008
3.22
thermal inertia
product of thermal conductivity, density and specific heat capacity
NOTE 1 When a material is exposed to a heat flux, the rate of increase in surface temperature depends strongly
on the value of the thermal inertia of the material. The surface temperature of a material with a low thermal inertia
rises relatively quickly when it is heated, and vice versa.
2 -1 -4 -2
NOTE 2 The typical units are J ⋅s ⋅m ⋅K .
3.23
upper flammability limit (UFL)
highest concentration of a flammable substance in air within which a self-propagating flame
can occur
4 Principles of ignitability
4.1 Gases
Ignition of a gas depends on how the gas is mixed with air. If the gas is mixed with air before
ignition, the subsequent reaction is known as premixed combustion. In a burner the
combustion is controlled, but if a large volume of a gas/air mixture is ignited a gas explosion
results.
In most fires ignition results in the development of diffusion flames where combustible gas
comes in contact with air without being previously mixed.
Gas mixtures can be ignited in two basic ways:
a) auto-ignition – where the temperature of all the gas mixture is raised, and
b) piloted ignition – where a local source of heat is introduced, e.g. a flame or an electrical
spark.
Some fires are the result of the ignition of a material which is already in the gaseous state,
but combustible gases can also be produced by the vaporization of liquids (see 4.2) or by the
pyrolysis of solids (see 4.3).
4.1.1 Flammability limits
Flame propagation cannot occur in a fuel/air gas mixture if the fuel concentration is too low or
too high. The limiting concentration values are known as the lower flammability limit (LFL) and
the upper flammability limit (UFL). These limits arise because flames need a minimum
temperature to exist. Too much air or fuel prevents the temperature being maintained at a
sufficiently high level. Flammability limits are normally expressed as the percentage of fuel, by
volume, in the fuel/air mixture.
4.1.2 Arc fires
Faults in some electrical equipment such as junction boxes and power transformers can result
in disruptive electrical discharges (electric arcs) which can pyrolyse insulation materials to
produce high temperature combustible gases. Such gases expand rapidly and in contact with
air can result in an explosion (see 5.3.3.4).
4.2 Liquids
4.2.1 Introduction
With the exception of some unstable or reactive substances, liquids do not generally ignite.
Normally it is combustible vapour which ignites. The combustible vapour is produced by
vaporization of the liquid, and the vaporization process is dependent on the temperature and
chemical composition of the liquid.
4.2.2 Ignition parameters
Temperature is normally used to define the ignitability of a liquid. Three different temperatures
are used. These are the auto ignition temperature (see 3.1), the fire point (see 3.5) and the
flash point (see 3.13). Auto ignition refers to ignition in the absence of a localized heat

TS 60695-1-20 © IEC:2008 – 11 –
source. Flash point concerns momentary ignition. Fire point concerns sustained combustion
after ignition.
Several different test methods are used to measure these characteristic temperatures. The
measured temperature depends on the particular details of the test apparatus used. It is
therefore important to define the test method when quoting these parameters.
4.2.3 Insulating liquids
4.2.3.1 Flash point measurement
ISO 2719 (Pensky-Martens closed cup) is cited in IEC standards for the measurement of the
flash point of insulating liquids. It measures the flash point in a confined space and is
intended to detect minor amounts of volatile material. An alternative method is ISO 2592
(Cleveland open cup) which is used to measure the flash point over an open liquid surface.
The flash point measured by ISO 2592 is significantly lower than that measured by ISO 2719.
4.2.3.2 Cone calorimeter measurements
IEC 60695-8-3 is being developed to measure the quantity of heat released from burning
insulating liquids. The test specimen is exposed to a uniform heat flux in the presence of a
piloted ignition source. Ignition related properties can be defined as the time to ignition at a
specified heat flux, or the minimum incident heat flux that will support ignition.
4.3 Solids
4.3.1 Introduction
With some exceptions (see below) solids do not generally ignite. Normally it is combustible
vapour which ignites. The combustible vapour is produced by pyrolysis of the solid, and the
vaporization process is dependent on the temperature and chemical composition of the solid.
The exceptions to this general statement are:
– metals (see 4.3.3);
– some other non-metallic elements, for example carbon (see 4.3.4), sulphur and
phosphorous;
– certain reactive substances (see 4.3.5); and
– dust clouds (see 4.3.6).
4.3.2 Parameters affecting ignition
In the case of a solid, the generation of flammable volatiles from the material is function of the
temperature of that material. This is affected by the nature of the heat input which may be, for
example, a radiant heat flux, a convective heat flux, a conductive heat flux, an imposed flame,
a hot wire or a combination of these sources.
The ease of ignition will also depend on the chemical nature of the flammable volatiles, which
in turn will depend on the chemical nature of the solid.
The rate of heating of the material is a function of a number of properties of the solid:
a) thickness;
b) thermal conductivity, (k);
ρ);
c) density, (
d) specific heat, (c);
e) absorptivity (in the case of radiative heating).
In a thick test specimen, material below the surface is able to conduct heat away thus
reducing the rate of surface heating and increasing the resistance to ignition. In a thin
specimen, this cannot happen and so resistance to ignition is lower.

– 12 – TS 60695-1-20 © IEC:2008
This general rule does not, however, apply to most thermoplastic materials. These have a
tendency to melt away from the heat source (e.g. flame or hot-wire) often resulting in non-
ignition. This can result in giving a false impression of a high resistance to ignition. Because
of this behaviour special considerations should be given to the testing of the ignitability of
thermoplastics. The problems that can arise when thermoplastics are tested in standard fire
tests are discussed in ISO 10840.
ρ c, is known as 'thermal inertia'. If the thermal inertia is high, for example as in
The product, k
the case of a solid metal, the rate of surface heating will be relatively low and it will therefore
take a relatively long time for the ignition temperature to be reached. If the thermal inertia is
low, e.g. as in the case of some foamed plastics or low density combustible materials, the rate
of surface heating will be relatively high and it will therefore take a relatively short time for the
ignition temperature to be reached.
After ignition of the test specimen, flame propagation will occur if the flame transfers sufficient
heat flux, mostly as thermal radiation, ahead of the pyrolysis front so as to continue pyrolysis
and ignition at a sufficient rate.
The magnitude of the heat flux transferred ahead of the pyrolysis front depends on the heat
release rate of the test specimen and on whether there is a continuing imposed heat flux,
whereas the resistance to ignition is a function of the minimum ignition temperature of the test
specimen and the rate of heating of the surface.
4.3.3 Metals
When a metal burns in air the product of combustion is the metal oxide. Many metals have a
film of metal oxide on the surface which is formed from low temperature oxidation. The oxide
film cannot burn because it is already the product of the metal's oxidation and so before the
bulk metal can burn, the surface layer of oxide must be removed in some way.
Metals can be classified into three groups with respect to their ignition characteristics.
a) Metals that ignite at or below their melting point (for example iron and magnesium). These
metals all have melting points above 650 ºC. These metals generally do not form a
protective oxide layer.
b) Metals that ignite after they melt (for example aluminium, lead, tin and zinc). These metals
all have melting points below 660 ºC. These metals generally form a protective oxide
layer.
c) Metals of low reactivity which do not ignite (for example mercury, silver, gold and
platinum).
The ease of ignition is also governed by the surface area/volume ratio of the metal. Thin films
of metal and finely divided powders are much easier to ignite than bulk pieces of metal. This
is because the heat released by the oxidation process is proportional to the burning surface
area, whereas the initial removal of heat from the surface by conduction is proportional to the
volume of the metal.
4.3.4 Carbon (graphite) and carbonaceous char
4.3.4.1 Graphite
Pure carbon in the form of graphite can ignite in air above a temperature of about 800 ºC. In
the range 800 ºC to 1 200 ºC, non-flaming surface combustion (glowing combustion) is found
to occur. Above about 1 200 ºC flaming combustion occurs with a CO flame being observed.
4.3.4.2 Carbonaceous char
Carbonaceous chars are impure forms of carbon. Volatile content and porosity are two
important variables which contribute to the wide range of observed ignition temperatures. As
with graphite both flaming combustion and non-flaming combustion may be observed. Many
carbon containing materials tend to form a carbonaceous char on their surface when they
burn, and at the early stages of fire this char layer can, to some extent, protect the underlying

TS 60695-1-20 © IEC:2008 – 13 –
material. A correlation has been observed between ignition resistance, as measured by
limiting oxygen index, and char yield for a range of organic polymers[1] .
4.3.5 Reactive substances
In most fires the oxidising agent is the oxygen in air. However, in some materials the oxidising
agent, usually oxygen, is part of the molecular structure of the material or is mixed with the
solid fuel in the form of a solid oxidising agent. These materials are usually deliberately made
to be combustible or explosive. Some illustrative examples are:
– “blue touch paper” (cellulose and potassium nitrate);
– gunpowder (carbon, sulphur and potassium nitrate);
– cigarettes (tobacco and potassium nitrate);
– TNT (trinitrotoluene).
4.3.6 Dust clouds
Dust clouds are solid aerosols; suspensions of small solid particles in air or other gases, and
their ignition behaviour is more like that of a premixed gas than that of a solid.
5 Consideration for the selection of test methods
5.1 Introduction
Important factors to be considered when selecting the test method to be used include; the fire
scenario or scenarios of concern, the possible ignition sources, the type of test specimen, and
the type of test procedure and apparatus.
5.2 Fire scenario
The test method(s) selected should be relevant to the fire scenario of concern. Important
parameters to be considered include:
a) the geometry of the test specimen, including thickness and the presence of edges, corners
or joints;
b) any anisotropy;
c) the surface orientation;
d) the rate and direction of air flow;
e) the nature and position of the ignition source;
f) the magnitude and position of any external heat flux; and
g) whether the flammable material is a solid or a liquid.
5.3 Ignition sources
The ignition source used in a laboratory test should be relevant to the fire scenario of
concern. In the case of the fire hazard of electrotechnical equipment, two types of ignition
source are of concern:
a) from unusual localized, internal sources of ohmic heat within electrotechnical equipment
and systems;
b) from sources of flame or excessive heat which are external to electrotechnical equipment
and systems.
In both cases a possible type of ignition specific to electrotechnical equipment is arc ignition.
This is discussed in 5.3.3.
___________
Figures in square brackets refer to the bibliography.

– 14 – TS 60695-1-20 © IEC:2008
5.3.1 Internal sources
If the ignition source under evaluation is within a product or located inside a component or an
apparatus, suitable test methods are those which are able to simulate the overheating caused
by:
a) the internal metallic parts (e.g. electrical contacts, conductors, etc.);
b) a small flame with a low heat transfer, caused by combustion started within the product or
located inside the component or the apparatus under evaluation;
c) electrical arcs (see 5.3.3).
The following test methods can be used, as appropriate, to measure and describe the
properties of a material, product, component or apparatus in response to heat and/or flame
under controlled laboratory conditions.
ISO 871 specifies a laboratory method for determining the flash-ignition temperature and
spontaneous-ignition temperature of plastics using a hot-air furnace. It is one of a number of
methods in use for evaluating the resistance of plastics to the effects of ignition sources.
The glow wire test methods (IEC 60695-2-11, IEC 60695-2-12 and IEC 60695-2-13) simulate
the first cause of ignition due to overheating by contact with a heated part, without an open
flame.
IEC 60695-2-11 (GWT) applies to components or apparatus only. It provides a qualitative
evaluation of the ignition behaviour and, above the minimum ignition temperature, it provides
a pass/fail criterion by assessing the burning duration under specified temperature conditions.
IEC 60695-2-12 (GWFI) and IEC 60695-2-13 (GWIT) are suitable for the preselection of
insulating materials. The GWFI test is designed to assess the maximum temperature at which
a material, when ignited, has a limited duration of burning without spreading fire from the test
specimen. The GWIT test is designed to assess the resistance to ignition by measuring the
minimum ignition temperature.
IEC 60695-11-5 is suitable to simulate ignition by a small flame. It is applicable to
electrotechnical equipment, its sub-assemblies and components and to solid electrical
insulating materials or other combustible materials. This test evaluates the ignitability of a
given test specimen and measures its ability to self extinguish.
IEC 60695-11-10 and IEC 60695-11-20 each provide a slighty different test method. Both of
these test methods involve direct contact of an open flame onto the surface of the test
specimen. The materials are rated depending on the length of time they burn (or glow) after
removal of the test flame and whether or not flaming droplets are produced. In IEC 60695-11-
10 a 50 W test flame is used. In IEC 60695-11-20 the test flame is ten times larger and the
flame application time is longer. In both cases the test methods provide classification systems
which may be used for quality assurance, or the pre-selection of component materials of
products.
NOTE The scopes of IEC 60695-11-10 and IEC 60695-11-20 do not refer to the simulation of either internal or
external ignition.
IEC 60695-11-11 is suitable to simulate ignition by the heat flux from a small non-contacting
flame.
5.3.2 External sources
If the ignition source under evaluation is located outside the electrotechnical equipment,
suitable test methods are those which are able to simulate the thermal stress caused by:
a) direct impingement of an open flame upon the surface of the equipment;
b) direct contact of high thermal stress (overheated metallic part) on the surface of the
equipment;
c) indirect thermal heat flux
i) radiant,
TS 60695-1-20 © IEC:2008 – 15 –
ii) convective,
d) electrical arcs (see 5.3.3).
The methods described in 5.3.1 can also be used to simulate external ignition as well as
internal ignition. The difference is the location of the application of the thermal stress.
IEC 60695-11-5, which simulates ignition by a small flame (see 5.3.1) has gained acceptance
in evaluating external ignition sources such as open candle flames .
Additional test methods could be:
IEC 60695-11-10 and IEC 60695-11-20 – Both these test methods involve direct contact of an
open flame onto the surface of the test specimen.
NOTE The scopes of these standards do not refer to the simulation of either internal or external ignition.
The materials are rated depending on the length of time they burn
...