EN 60079-10-2:2015

SLOVENSKI STANDARD
01-junij-2015
1DGRPHãþD
SIST EN 60079-10-2:2009
Eksplozivne atmosfere - 10-2. del: Razvrstitev prostorov - Eksplozivne prašne
atmosfere (IEC 60079-10-2:2015)
Explosive atmospheres -- Part 10-2: Classification of areas - Combustible dust
atmospheres (IEC 60079-10-2:2015)
Explosionsgefährdete Bereiche - Teil 10-2: Einteilung der Bereiche -
Staubexplosionsgefährdete Bereiche (IEC 60079-10-2:2015)
Atmosphéres explosives - Partie 10-2: Classement des emplacements - Atmosphères
explosives poussiéreuses (IEC 60079-10-2:2015)
Ta slovenski standard je istoveten z: EN 60079-10-2:2015
ICS:
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 60079-10-2

NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2015
ICS 29.260.20 Supersedes EN 60079-10-2:2009
English Version
Explosive atmospheres - Part 10-2: Classification of areas -
Explosive dust atmospheres
(IEC 60079-10-2:2015)
Atmosphéres explosives - Partie 10-2: Classement des Explosionsgefährdete Bereiche - Teil 10-2: Einteilung der
emplacements - Atmosphères explosives poussiéreuses Bereiche - Staubexplosionsgefährdete Bereiche
(IEC 60079-10-2:2015) (IEC 60079-10-2:2015)
This European Standard was approved by CENELEC on 2015-02-20. 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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, 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: Avenue Marnix 17, B-1000 Brussels
© 2015 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60079-10-2:2015 E
Foreword
The text of document 31J/244/FDIS, future edition 2 of IEC 60079-10-2, prepared by SC 31J "Classification
of hazardous areas and installation requirements" of IEC/TC 31 "Equipment for explosive atmospheres" was
submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN 60079-10-2:2015.

The following dates are fixed:
(dop) 2015-11-20
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2018-02-20
• latest date by which the national
standards conflicting with the
document have to be withdrawn
This document supersedes EN 60079-10-2:2009.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 60079-10-2:2015 was approved by CENELEC as a European
Standard without any modification.
IEC 60079-2 NOTE Harmonized as EN 60079-2.
IEC 60079-11 NOTE Harmonized as EN 60079-11.
IEC 60079-14 NOTE Harmonized as EN 60079-14.
IEC 60079-28 NOTE Harmonized as EN 60079-28.
IEC 60079-18 NOTE Harmonized as EN 60079-18.
IEC 60079-31 NOTE Harmonized as EN 60079-31.
IEC 60079-32-2 NOTE Harmonized as EN 60079-32-2.

- 3 - EN 60079-10-2:2015
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
NOTE 1 When 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 60079-0 (mod) -  Explosive atmospheres -- Part 0: Equipment - EN 60079-0 -
General requirements
+A11 2013
IEC 60079-10-1 -  Explosive atmospheres -- Part 10-1: EN 60079-10-1 -
Classification of areas - Explosive gas
atmospheres
ISO/IEC 80079-20-2 -  Explosive atmospheres - Part 20-2: Material - -
characteristics - Combustible dusts test
methods
IEC 60079-10-2 ®
Edition 2.0 2015-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Explosive atmospheres –
Part 10-2: Classification of areas – Explosive dust atmospheres

Atmosphères explosives –
Partie 10-2: Classement des emplacements – Atmosphères explosives

poussiéreuses
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.260.20 ISBN 978-2-8322-2195-2

– 2 – IEC 60079-10-2:2015 © IEC 2015
CONTENTS
FOREWORD . 4
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 9
3 Terms and definitions . 9
4 Area classification . 12
4.1 General . 12
4.2 Area classification procedure for explosive dust atmospheres . 13
4.3 Competence of personnel . 14
5 Sources of release. 14
5.1 General . 14
5.2 Dust containment . 14
5.3 Identification and grading of sources of release . 14
6 Zones . 15
6.1 General . 15
6.2 Extent of zones . 15
6.2.1 General . 15
6.2.2 Zone 20 . 15
6.2.3 Zone 21 . 16
6.2.4 Zone 22 . 16
7 Dust layers . 16
8 Documentation . 17
8.1 General . 17
8.2 Drawings, data sheets and tables . 17
8.2.1 Content of documents . 17
8.2.2 Preferred Symbol key for area classification zones . 18
Annex A (informative) Area classification examples . 19
A.1 Examples of zones . 19
A.1.1 General . 19
A.1.2 Zone 20 . 19
A.1.3 Zone 21 . 19
A.1.4 Zone 22 . 19
A.2 Bag emptying station within a building and without exhaust ventilation . 20
A.3 Bag emptying station with exhaust ventilation . 21
A.4 Cyclone and filter with clean outlet outside building . 21
A.5 Drum tipper within a building without exhaust ventilation . 22
Annex B (informative) Housekeeping . 24
B.1 Introductory remarks . 24
B.2 Levels of housekeeping . 24
Annex C (informative) Hybrid mixtures . 26
C.1 General . 26
C.2 Ventilation. 26
C.3 Explosive limits . 26
C.4 Chemical reactions . 26
C.5 Minimum ignition parameters . 26

IEC 60079-10-2:2015 © IEC 2015 – 3 –
C.6 Final classification . 26
Bibliography . 27

Figure 1 – Identification of zones on drawings . 18
Figure A.1 – Bag emptying station within a building and without exhaust ventilation . 20
Figure A.2 – Bag emptying station with exhaust ventilation . 21
Figure A.3 – Cyclone and filter with clean outlet outside building . 22
Figure A.4 – Drum tipper within a building without exhaust ventilation . 23

Table 1 – Designation of zones depending on presence of dust . 16

– 4 – IEC 60079-10-2:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 10-2: Classification of areas –
Explosive 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
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 60079-10-2 has been prepared by subcommittee 31J:
Classification of hazardous areas and istallation requirements, of IEC technical committee 31:
Equipment for explosive atmospheres.
This second edition of IEC 60079-10-2 cancels and replaces the first edition of
IEC 60079-10-2 published in 2009. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
IEC 60079-10-2:2015 © IEC 2015 – 5 –
Type
Explanation of the significance of the changes Clause Minor and Extension Major
editorial technical
changes changes
Definition of “atmospheric conditions” deleted 3 X
Definition of “combustible dust” aligned with other
3.4 X
documents per recommendations of WG 28
Editorial change to definition of “explosive dust atmosphere”
to delete mention of flyings, since the definition of dust 3.5 X
according to 60079-10-2 includes flyings.
Definition of “combustible flyings” aligned with other
3.8 X
documents per recommendations of WG 28
Definition of “continuous formation of a dust cloud” added 3.14 X
Definition of “catastrophic failure” added 3.20 X
Definition of “ignition temperature of a dust layer” aligned
with other documents per recommendations of WG 28 and 3.22 X
to change reference from 61241-2-1 to 80079-20-2
Definitions of “zone 20, zone 21 and zone 22” added. 3.25.1
These were previously incorrectly included in the body of
3.25.2 X
the document.
3.25.3
Dust cloud density and concentration added as factors to
4.1 X
consider for a release
Wording changed to require EPL to be noted on area
4.1 X
classification drawing
Notes 1 and 3 changed to normative text 4.1 X
Reference to published sources for dust characteristics
4.2 X
deleted
Reference to 80079-20-2 added 4.2 a) X
Section on competence of personnel added 4.3 X
Note on verification dossier deleted 5.2 X
Example added for continuous grade of release, zone
5.3 X
information moved to Clause 6
Paragraph added about dust layers being raised into a
7 X
cloud
EPLs added to list for documentation, note added warning
8.1 X
of variability in published dust data
Symbol keys are identified as preferred 8.2 X
Note added to zone 21 and zone 22 clause about distance
Annex A X
around source of release
Zone 22 paragraph added to this example, and figure
A.2 X
modified to show Zone 22 location
Annex B on hot surfaces deleted Annex B in
previous X
edition
Annex D on explanation of EPLs deleted Annex D in
previous X
edition
Annex on hybrid mixtures added Annex C X

– 6 – IEC 60079-10-2:2015 © IEC 2015
Explanation of the types of significant changes:
– Clarification
– Decrease of technical requirements
1. Minor and editorial changes:
– Minor technical change
– Editorial corrections
These are changes which modify requirements in an editorial or a minor technical way. They include changes of
the wording to clarify technical requirements without any technical change, or a reduction in the level of existing
requirement.
2. Extension:
– Addition of technical options
These are changes which add new or modify existing technical requirements, in a way that new options are
given, but without increasing the requirements that are fully compliant with the previous standard. Therefore,
these will not have to be considered for existing area classifications in conformity with the preceding edition.
– Addition of technical requirements
3. Major technical changes:
– Increase of technical requirements
These are changes to technical requirements (addition, increase of the level or removal) made in a way that an
existing area classification in conformity with the preceding edition will not always be able to fulfil the
requirements given in the later edition. These changes have to be considered for existing area classifications in
conformity with the preceding edition.

The text of this standard is based on the following documents:
FDIS Report on voting
31J/244/FDIS 31J/248/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 stability date indicated on the IEC website 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.
IEC 60079-10-2:2015 © IEC 2015 – 7 –
INTRODUCTION
Dusts, as defined in this standard, are hazardous because when they are dispersed in air by
any means they may 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 for the
process of identification and classification of hazardous areas.
This standard contains an informative Annex A giving examples for classifying areas.

– 8 – IEC 60079-10-2:2015 © IEC 2015
EXPLOSIVE ATMOSPHERES –
Part 10-2: Classification of areas –
Explosive 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 other general
considerations for dust layers are 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 might
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
(see Note 1).
NOTE 1 Atmospheric conditions 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 materials.
It does not apply to
– underground mining areas,
– dusts of explosives that do not require atmospheric oxygen for combustion such as
pyrophoric substances, propellants, pyrotechnics, munitions, peroxides, oxidizers, water-
reactive elements or compounds, or other similar materials.
– catastrophic failures which are beyond the concept of abnormality dealt with in this
standard,
– any risk arising from an emission of toxic gas from the dust.
This standard does not apply to where a hazard might arise due to the presence of flammable
gas or vapour, but the principles may be used in the assessment of a hybrid mixture (see also
IEC 60079-10-1).
NOTE 2 Additional guidance on hybrid mixtures is provided in Annex C.
This standard does not take into account the effects of consequential damage following a fire
or an explosion.
IEC 60079-10-2:2015 © IEC 2015 – 9 –
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas
atmospheres
ISO/IEC 80079-20-2, Explosive Atmospheres – Part 20-2: Material Characteristics –
Combustible dusts test methods
3 Terms and definitions
For the purposes of this document, the 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
hybrid mixture
mixture of a flammable gas or vapour with a dust
3.3
dust
generic term including both combustible dust and combustible flyings
3.4
combustible dust
finely divided solid particles, 500 µm or less in nominal size, which may form an explosive
mixture with air at atmospheric pressure and normal temperatures
Note 1 to entry: This includes dust and grit as defined in ISO 4225.
Note 2 to entry: The term solid particles is intended to address particles in the solid phase and not the gaseous or
liquid phase, but does not preclude a hollow particle.
Note 3 to entry: Materials passing a U.S. No. 40 Standard sieve as defined in ASTM E 11-04 are considered to
meet the 500 µm criterion.
Note 4 to entry: Combustible dust test methods can be found in ISO/IEC 80079-20-2.
3.5
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust,
which, after ignition, permits self-sustaining propagation
______________
To be published.
– 10 – IEC 60079-10-2:2015 © IEC 2015
3.6
conductive dust
combustible dust with electrical resistivity equal to or less than 10 Ωm
Note 1 to entry: Conductive dust is classified as Group IIIC.
3.7
non-conductive dust
combustible dust with electrical resistivity greater than 10 Ωm
Note 1 to entry: Non-conductive dust is classified as Group IIIB.
3.8
combustible flyings
solid particles including fibers, greater than 500 µm in nominal size, which may form an
explosive mixture with air at atmospheric pressure and normal temperatures
Note 1 to entry: Examples of flyings include rayon, cotton (including cotton linters and cotton waste) sisal, jute,
hemp, cocoa fiber, okum and waste kapok.
Note 2 to entry: Combustible flyings are classified as Group IIIA.
3.9
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 to entry: 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 to entry: The potential of creating an explosive dust cloud from a dust layer also needs to be considered.
3.10
non-hazardous area (dust)
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
3.11
dust containment
process equipment housing which is intended to handle, process, transport or store materials
inside of it, while minimizing the risk of the release of dust to the surrounding atmosphere
3.12
source of dust release
point or location from which dust may be released into the atmosphere
Note 1 to entry: The source of dust release can be from a dust containment or from a dust layer.
3.13
continuous grade of release
release which is continuous or is expected to occur frequently or for long periods
3.14
continuous formation of a dust cloud
locations in which a dust cloud may exist continuously, or may be expected to continue for
long periods or for short periods which occur frequently

IEC 60079-10-2:2015 © IEC 2015 – 11 –
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 1 to entry: Minor releases of dust which may form a cloud or layer (e.g. releases from filters) can be part of
normal operation.
3.19
abnormal operation
process-linked malfunctions that occur infrequently
3.20
catastrophic failure
occurrence which exceeds the design parameters of the process plant and control system
resulting in major release of flammable material
Note 1 to entry: Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a
pneumatic conveyor.
3.21
equipment (for explosive atmospheres)
general term including apparatus, fittings, devices, components, and the like used as a part
of, or in connection with, an installation in an explosive atmosphere
3.22
ignition temperature of a dust layer
lowest temperature of a surface at which ignition occurs in a dust on the surface
Note 1 to entry: The ignition temperature of a dust layer may be determined by the test method given in
ISO/IEC 80079-20-2.
3.23
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 1 to entry: The ignition temperature of a dust cloud may be determined by the test method given in ISO/IEC
80079-20-2.
3.24
verification dossier
set of documents showing the compliance of electrical equipment and installations
Note 1 to entry: Requirements for a ‘verification dossier’ are given in IEC 60079-14.

– 12 – IEC 60079-10-2:2015 © IEC 2015
3.25
zones
3.25.1
Zone 20
a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present
continuously, or for long periods or frequently
3.25.2
Zone 21
a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is likely to
occur in normal operation occasionally
3.25.3
Zone 22
area in which an explosive dust atmosphere, in the form of a cloud of combustible dust in air,
is not likely to occur in normal operation but, if it does occur, will persist for a short period
only
Note 1 to entry: The potential of creating an explosive dust cloud from a dust layer also needs to be considered.
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 explosive range.
Depending on the circumstances, not every source of release will necessarily produce an
explosive dust atmosphere. Dust clouds are also rarely of uniform density and consideration should
be given to possible variances in concentration within a cloud for any condition or release.
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.
Since explosive dust clouds and dust layers may exist, any source of ignition should be
avoided.
If the source of ignition cannot be avoided, then measures shall be taken to reduce the
likelihood of dust and/or ignition sources so that the likelihood of coincidence is so small as to
make the risk negligible.
NOTE 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, explosion suppression or explosion isolation.

IEC 60079-10-2:2015 © IEC 2015 – 13 –
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 may justify the use of equipment
with a lower equipment protection level than normally required.
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. Considerations for dust layers are described in
Clause 7.
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 ISO/IEC 80079-20-2.
• Material characteristics for the dusts that are present. These may be obtained from a
variety of published sources, a process specialist or by testing. Characteristics that are
obtained from published sources should be validated for the particular application, since
there are often significant variations in dust characteristic values from one data source to
another.
• Nature of dust releases from particular process sources. Specialist engineering knowledge
may be required for this information.
• Operational and maintenance procedures 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 dust 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. Parameters such
as particle size, moisture content, cloud and layer minimum ignition temperature and
electrical resistivity shall be considered. The appropriate dust group; Group IIIA for
combustible flyings, Group IIIB for non-conductive dust, or Group IIIC for conductive dust
shall be identified.
NOTE Information on dust characteristics can be found in ISO/IEC 80079-20-2.
b) The second step is to identify items of equipment where explosive dust mixtures may be
contained or sources of dust release can be present, as given in Clause 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 have been taken that the zones can be identified and their
boundaries 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, 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.
– 14 – IEC 60079-10-2:2015 © IEC 2015
Because this standard covers a wide range of circumstances, no exact identification of
necessary measures can be given for each individual case. It is important, therefore, that the
recommended procedure should be carried out by personnel having knowledge of the
principles of area classification, the process material used, the specific plant involved and its
functioning.
4.3 Competence of personnel
The area classification should be carried out by those who are competent and understand the
relevance and significance of the characteristics of dust and those who are familiar with the
process and the equipment, along with safety, electrical, mechanical, and other qualified
engineering personnel.
NOTE These elements are covered in several personnel certification schemes, such as the IECEx Unit of
Competence Ex002 according to IECEx OD 504.
5 Sources of release
5.1 General
Explosive dust atmospheres are formed from sources of dust release. A source of dust
release is a point or location from which dust can be released or raised, such that an
explosive dust atmosphere can be formed. This definition includes layers of dust capable of
being dispersed to form a dust cloud.
Depending on the circumstances, not every source of release will necessarily produce an
explosive dust atmosphere. However, a dilute or small continuous source of release in time
can produce a dust layer.
The conditions need to be identified under which process equipment, process steps or other
actions expected in plants, can form explosive dust atmospheres or create dust layers. It is
necessary to consider separately the inside and outside of a dust containment.
5.2 Dust containment
Inside a dust containment, dust is not released into the outside atmosphere but as part of the
process, continuous dust clouds may form inside the containment. These clouds may exist
continuously or may be expected to continue for long periods or for short periods. The
frequency of their appearance depends on the process cycle. The equipment shall be studied
for normal operation, abnormal operation and in the start up and shut-down conditions so that
the incidence of cloud and layer presence can be identified and the results of this study shall
be included in the verification dossier. Where layers are formed, these should be noted (see
Clause 7 for dust layers).
5.3 Identification and grading of sources of release
Outside the dust containment, many factors can influence the area classification. Where
higher than atmospheric pressures are used within the dust containment (e.g. positive
pressure pneumatic transfer) dust can easily be blown out of leaking equipment. In the case
of negative pressure within the dust containment, the likelihood of formation of dusty areas
outside the equipment is very low. Dust particle size, moisture content and, where applicable,
factors such as transport velocity, dust extraction rate and fall height can influence release
rate potential. Once the process potential for release is known, each source of release shall
be identified and its grade or grades of release determined.
Grades of release are as follows:
– continuous grade of release:

IEC 60079-10-2:2015 © IEC 2015 – 15 –
release that exists continuously, or may be expected to continue for long periods, or for
short periods that occur frequently. For example, the inside of a mixing vessel or a storage
silo that is filled and emptied often;
– primary grade of release:
release that can be expected to occur periodically or occasionally during normal operation.
For example, the close vicinity around an open bag filling or emptying point;
– secondary grade of release:
release that is not expected to occur in normal operation and, if it does occur, is likely to
do so only infrequently and for short periods. For example, a dust handling plant where
deposits of dust are present.
Consideration of catastrophic failures is not required in assessing potential sources of
release. For example some of the items that should not be regarded as sources of release
during normal and abnormal operation include:
– pressure vessels, the main structure of the shell including closed nozzles and man-holes;
– pipes, ducting and trunking without joints;
– valve glands and flanged joints, provided that in the design and construction, adequate
consideration has been given to the prevention of the release of dust.
6 Zones
6.1 General
Areas classified for explosive dust atmosphere are divided into zones, which are identified
according to the frequency and duration of the occurrence of explosive dust atmosphere.
Some examples of zones are given in Annex A. Layers, deposits and heaps of dust shall be
considered as ‘any other source’ which can form an explosive dust atmosphere.
6.2 Extent of zones
6.2.1 General
The extent of a zone for explosive dust atmospheres is defined as the distance in any
direction from the edge of a source of dust release to the point where the hazard associated
with that zone is considered to no longer exist.
Explosive dust atmospheres from a dust cloud would normally be deemed not to exist if the
dust concentration is a suitable safety margin less than the minimum dust concentration
required for an explosive dust atmosphere to exist. Consideration should be given to the fact
that fine dust can be carried from a source of release by air movement within a building.
Where the classification gives rise to small unclassified areas between classified areas, the
classification should be extended to the full area. For Zone 21 and Zone 22 areas located
outside buildings (open air), the zones can be altered due to weather effects such as wind,
rain, etc. For out
...