IEC 60079-10-2:2009
(Main)Explosive atmospheres - Part 10-2: Classification of areas - Combustible dust atmospheres
Explosive atmospheres - Part 10-2: Classification of areas - Combustible dust atmospheres
IEC 60079-10-2:2009 is concerned with the identification and classification of areas where explosive dust atmospheres and combustible dust layers are present, in order to permit the proper assessment of ignition sources in such areas. The principles of this standard can also be followed when combustible fibres or flyings may cause a hazard. This standard is intended to be applied where there can be a risk due to the presence of explosive dust atmospheres or combustible dust layers under normal atmospheric conditions. This first edition of IEC 60079-10-2 cancels and replaces the first edition of IEC 61241-10 published in 2004. The significant technical changes with respect to IEC 61241-10 are:
- the hazards presented by dust have been clarified;
- dust groups have been introduced;
- Annex D explaining Equipment Protection Levels (EPLs) has been introduced;
- 1 m of usual extent of zone 22 beyond zone 21 has been expanded to 3 m.
Atmosphères explosives - Partie 10-2: Classement des emplacements - Atmosphères explosives poussiéreuses
La CEI 60079-10-2:2009 traite de l'identification et de la classification des emplacements où des atmosphères explosives poussiéreuses et des couches de poussières combustibles sont présentes, afin de permettre une évaluation appropriée des sources d'inflammation à utiliser dans de tels emplacements. Les principes de la présente norme peuvent également être suivis lorsque des fibres ou particules volatiles et combustibles sont une source de danger. La présente norme est destinée à être appliquée lorsqu'il y a danger dû à la présence d'atmosphère poussiéreuse explosive ou de couches de poussières combustibles dans des conditions atmosphériques normales. Cette première édition de la CEI 60079-10-2 annule et remplace la première édition de la CEI 61241-10 publiée en 2004. Les principales modifications techniques apportées par rapport à la première édition de la CEI 61241-10 sont les suivantes:
- les dangers liés aux poussières ont été clarifiés;
- les groupes de poussières ont été introduits;
- l'Annexe D expliquant les niveaux de protection du matériel (EPLs) a été créée;
- l'étendue usuelle de 1 m de la zone 22 au delà de la zone 21 a été étendue à 3 m.
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Standards Content (Sample)
IEC 60079-10-2
®
Edition 1.0 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 10-2: Classification of areas – Combustible dust atmospheres
Atmosphères explosives –
Partie 10-2: Classement des emplacements – Atmosphères explosives
poussiéreuses
IEC 60079-10-2:2009
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IEC 60079-10-2
®
Edition 1.0 2009-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 10-2: Classification of areas – Combustible dust atmospheres
Atmosphères explosives –
Partie 10-2: Classement des emplacements – Atmosphères explosives
poussiéreuses
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 29.260.20 ISBN 978-2-88910-044-6
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative references .6
3 Terms and definitions .7
4 Area classification .9
4.1 General .9
4.2 Area classification procedure for explosive dust atmospheres .10
5 Sources of release .11
5.1 General .11
5.2 Dust containment .11
5.3 Identification and gradation of sources of release.11
6 Zones .12
6.1 General .12
6.2 Zones.12
6.3 Extent of zones .13
6.3.1 General .13
6.3.2 Zone 20.13
6.3.3 Zone 21.13
6.3.4 Zone 22.14
7 Dust layer hazard .14
8 Documentation .14
8.1 General .14
8.2 Drawings, data sheets and tables.15
Annex A (informative) Area classification application .17
Annex B (informative) Risk of fire from hot surface ignition of dust layer .22
Annex C (informative) Housekeeping .23
Annex D (informative) Introduction of an alternative risk assessment method
encompassing ‘equipment protection levels’ for Ex equipment .25
Bibliography.30
Figure 1 – Identification of zones on drawings .16
Figure A.1 – Bag emptying station within a building and without exhaust ventilation .18
Figure A.2 – Bag emptying station with exhaust ventilation .19
Figure A.3 – Cyclone and filter with clean outlet outside building .20
Figure A.4 – Drum tipper within a building without exhaust ventilation.21
Table 1 – Designation of zones depending on presence of dust .12
Table D.1 – Traditional relationship of EPLs to zones (no additional risk assessment) .27
Table D.2 – Description of risk of ignition protection provided .28
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60079-10-2 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
EXPLOSIVE ATMOSPHERES –
Part 10-2: Classification of areas –
Combustible dust atmospheres
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
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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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.
International Standard IEC 60079-10-2 has been prepared by subcommittee 31J:
Classification of hazardous areas and installation requirements, of IEC technical committee
31: Equipment for explosive atmospheres.
This first edition of IEC 60079-10-2 cancels and replaces the first edition of IEC 61241-10
published in 2004. This edition constitutes a technical revision.
The significant technical changes with respect to the first edition of IEC 61241-10 are as
follows:
• the hazards presented by dust have been clarified;
• dust groups have been introduced;
• Annex D explaining Equipment Protection Levels (EPLs) has been introduced;
• 1 m of usual extent of zone 22 beyond zone 21 has been expanded to 3 m.
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The text of this standard is based on the following documents:
FDIS Report on voting
31J/166/FDIS 31J/168/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 60079 series, under the general title Explosive atmospheres, can
be found on the IEC website.
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
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
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60079-10-2 © IEC:2009 – 5 –
INTRODUCTION
Dusts, as defined in this standard, are hazardous because when they are dispersed in air by
any means, they form potentially explosive atmospheres. Furthermore, layers of dust may
ignite and act as ignition sources for an explosive atmosphere.
This part of IEC 60079 gives guidance on the identification and classification of areas where
such hazards from dust can arise. It sets out the essential criteria against which the ignition
hazards can be assessed and gives guidance on the design and control parameters which
can be used in order to reduce such a hazard. General and special criteria are given, with
examples, for the procedure used to identify and classify areas.
This standard contains an informative Annex A giving practical examples for classifying areas.
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EXPLOSIVE ATMOSPHERES –
Part 10-2: Classification of areas –
Combustible dust atmospheres
1 Scope
This part of IEC 60079 is concerned with the identification and classification of areas where
explosive dust atmospheres and combustible dust layers are present, in order to permit the
proper assessment of ignition sources in such areas.
In this standard, explosive dust atmospheres and combustible dust layers are treated
separately. In Clause 4, area classification for explosive dusts clouds is described, with dust
layers acting as one of the possible sources of release. In Clause 7, the hazard of dust layer
ignition is described.
The examples in this standard are based on a system of effective housekeeping being
implemented in the plant to prevent dust layers from accumulating. Where effective
housekeeping is not present, the area classification includes the possible formation of
explosive dust clouds from dust layers.
The principles of this standard can also be followed when combustible fibres or flyings may
cause a hazard.
This standard is intended to be applied where there can be a risk due to the presence of
explosive dust atmospheres or combustible dust layers under normal atmospheric conditions.
It does not apply to
– underground mining areas,
– areas where a risk can arise due to the presence of hybrid mixtures,
– dusts of explosives that do not require atmospheric oxygen for combustion, or to
pyrophoric substances,
– catastrophic failures which are beyond the concept of abnormality dealt with in this
standard (see Note 1),
– any risk arising from an emission of flammable or toxic gas from the dust.
This standard does not take into account the effects of consequential damage following a fire
or an explosion.
NOTE 1 Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a pneumatic
conveyor.
NOTE 2 In any process plant, irrespective of size, there can be numerous sources of ignition apart from those
associated with equipment. Appropriate precautions will be necessary to ensure safety in this context, but these
are outside the scope of this standard.
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.
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60079-10-2 © IEC:2009 – 7 –
IEC 60079-0, Explosive Atmospheres – Part 0: Equipment – General requirements
3 Terms and definitions
For the purposes of this document, terms and definitions given in IEC 60079-0 and the
following apply.
NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
3.1
area
three-dimensional region or space
3.2
atmospheric conditions
(surrounding conditions)
conditions that include variations in pressure and temperature above and below reference
levels of 101,3 kPa (1 013 mbar) and 20 °C (293 K), provided that the variations have a
negligible effect on the explosive properties of the combustible dust
3.3
hybrid mixture
mixture of flammable substances in different physical states, with air
NOTE An example of a hybrid mixture is a mixture of methane, coal dust and air.
3.4
dust
generic term including both combustible dust and combustible flyings
3.5
combustible dust
finely divided solid particles, 500 μm or less in nominal size, which may be suspended in air,
may settle out of the atmosphere under their own weight, can burn or glow in air, and may
form explosive mixtures with air at atmospheric pressure and normal temperatures
NOTE 1 This definition may also include dust and grit as defined in ISO 4225.
NOTE 2 The term ‘solid particle’ is intended to address particles in the solid phase and not the gaseous or liquid
phase, but does not preclude a hollow particle.
3.6
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust,
or flyings in which, after ignition, permits self-sustaining flame propagation
3.7
conductive dust
combustible dust with electrical resistivity equal to or less than 103 Ωm
3.8
non-conductive dust
combustible dust with electrical resistivity greater than 103 Ωm
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3.9
combustible flyings
solid particles, including fibres, greater than 500 μm in nominal size, which may be suspended
in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and
may form explosive mixtures with air at atmospheric pressure and normal temperatures
NOTE Examples of fibres and flyings include rayon, cotton (including cotton linters and cotton waste), sisal, jute,
hemp, cocoa fibre, oakum, and baled waste kapok.
3.10
hazardous area (dust)
area in which combustible dust, in the form of a cloud is present, or may be expected to be
present, in quantities such as to require special precautions for the construction, installation
and use of equipment
NOTE 1 Hazardous areas are divided into zones based upon the frequency and duration of
the occurrence of explosive dust atmospheres (see 6.2 and 6.3).
NOTE 2 The potential of creating an explosive dust cloud from a dust layer also needs to be considered.
3.11
non-hazardous area (dust)
an area in which combustible dust in the form of a cloud is not expected to be present in
quantities such as to require special precautions for the construction, installation and use of
equipment
3.12
dust containment
process equipment housing which is intended to handle, process, transport or store materials
inside of it, while preventing the release of combustible dust to the surrounding atmosphere
3.13
source of dust release
point or location from which combustible dust can be released into the atmosphere
NOTE This can be from a dust containment or a dust layer.
3.14
continuous grade of release
release which is continuous or is expected to occur frequently or for long periods
3.15
primary grade of release
release which can be expected to occur periodically or occasionally during normal operation
3.16
secondary grade of release
release which is not expected to occur in normal operation and, if it does occur, is likely to do
so only infrequently and for short periods
3.17
extent of zone
distance in any direction from the edge of a source of release to the point where the hazard
associated with the release is considered to exist no longer
3.18
normal operation
operation of equipment conforming electrically and mechanically with its design specification
and used within the limits specified by the manufacturer
NOTE Minor releases of dust which may form a cloud or layer (e.g. releases from filters) can be part of normal
operation.
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60079-10-2 © IEC:2009 – 9 –
3.19
abnormal operation
process-linked malfunctions that occur infrequently
3.20
equipment (for explosive atmospheres)
general term including apparatus, fittings, devices, components, and the like used as a part
of, or in connection with, an electrical installation in an explosive atmosphere
3.21
ignition temperature of a dust layer
lowest temperature of a hot surface at which ignition occurs in a dust layer of specified
thickness on a hot surface
NOTE The ignition temperature of a dust layer may be determined by the test method given in IEC 61241-2-1.
3.22
ignition temperature of a dust cloud
lowest temperature of the hot inner wall of a furnace at which ignition occurs in a dust cloud in
air contained therein
NOTE The ignition temperature of a dust cloud may be determined by the test method given in IEC 61241-2-1.
3.23
verification dossier
set of documents showing the compliance of electrical equipment and installations
NOTE Requirements for a ‘verification dossier’ are given in IEC 60079-14.
4 Area classification
4.1 General
This standard adopts the concept, similar to that used for flammable gases and vapour, of
using area classification to give an assessment of the likelihood of an explosive dust
atmosphere occurring.
Dusts form explosive atmospheres only at concentrations within the explosion range.
Although a cloud with a very high concentration may not be explosive, the danger
nevertheless exists that, should the concentration fall, it may enter the explosion range.
Depending on the circumstances, not every source of release will necessarily produce an
explosive dust atmosphere.
Dusts that are not removed by mechanical extraction or ventilation, settle out at a rate
depending on properties, such as particle size, into layers or accumulations. It shall be taken
into account that a dilute or small continuous source of release, in time, is able to produce a
potentially hazardous dust layer.
The hazards presented by dusts are as follows:
– the formation of a dust cloud from any source of release, including a layer or
accumulation, to form an explosive dust atmosphere (see Clause 5);
– the formation of dust layers, which are not likely to form a dust cloud, but may ignite due
to self-heating or exposure to hot surfaces or thermal flux and cause a fire hazard or over-
heating of equipment. The ignited layer may also act as an ignition source for an explosive
atmosphere (see Clause 7).
Since explosive dust clouds and dust layers may exist, any source of ignition should be
avoided.
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Subsequent to the completion of the area classification, a risk assessment may be carried out
to assess whether the consequences of ignition of an explosive atmosphere requires the use
of equipment of a higher equipment protection level (EPL) or justify the use of equipment with
a lower equipment protection level than normally required. The EPL requirements may be
recorded, as appropriate, on the area classification drawings to allow proper assessment of
ignition sources.
NOTE 1 If this cannot be done, then measures should be taken to reduce the likelihood of dust and/or ignition
sources so that the likelihood of coincidence is so small as to be acceptable.
NOTE 2 In some cases, where the risk of explosion cannot be completely avoided, it can be necessary to employ
some form of explosion protection such as explosion venting or explosion suppression.
NOTE 3 In this standard, explosive dust atmospheres and dust layers are treated separately. In this clause, area
classification for explosive dust clouds is described, with dust layers acting as one of the possible sources of
release. The hazard of dust layer ignition is described in Clause 7.
NOTE 4 Additional information on EPLs is given in Annex D.
4.2 Area classification procedure for explosive dust atmospheres
Area classification is based on a number of factors and may require informed input from a
number of sources. These factors include:
• Whether the dust is combustible or not. Dust combustibility can be confirmed by laboratory
tests to the future IEC 60079-20-2.
• Material characteristics for the process concerned. These should be obtained from a
process specialist.
• Nature of release from particular items of plant. Specialist engineering knowledge may be
required for this information.
• Operational and maintenance regime for the plant, including housekeeping.
• Other equipment and safety information.
Close co-operation is necessary from specialists in safety and equipment. Although the
definitions for zones deal only with the cloud risk, layers that can be disturbed to form a dust
cloud shall also be considered. The procedure for identifying zones is as follows.
a) The first step is to identify whether the material is combustible and, for the purpose of
assessment of ignition sources, determine the material characteristics, such as particle
size, moisture content, cloud and layer minimum ignition temperature and electrical
resistivity, and the appropriate dust group, Group IIIA for combustible flyings, Group IIIB
for non-conductive dust, or Group IIIC for conductive dust.
b) The second step is to identify where dust containment or sources of dust release can be
present, as given inClause 5. It may be necessary to consult process line diagrams and
plant layout drawings. This step should include the identification of the possibility of the
formation of dust layers as given in Clause 7.
c) The third step is to determine the likelihood that dust will be released from those sources
and thus, the likelihood of explosive dust atmospheres in various parts of the installation
as given in 5.3.
It is only after these steps that the zones can be identified and their extents defined. The
decisions on the zone types and extent and the presence of dust layers shall be documented,
usually on an area classification drawing. These documents are used subsequently as the
basis for the assessment of ignition sources.
The reasons for the decisions taken should be recorded in notes of the area classification
study, to facilitate understanding at future area classification reviews. Reviews of the area
classification shall take place following changes to the process or changes to process
materials or if dust emission becomes more common due to deterioration of the plant. It is
expected that a review be made following the commissioning of a plant or process, and
thereafter on a periodic basis.
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60079-10-2 © IEC:2009 – 11 –
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