EN 60079-10-1:2015

SLOVENSKI STANDARD
01-marec-2016
1DGRPHãþD
SIST EN 60079-10-1:2009
Eksplozivne atmosfere - 10-1. del: Razvrstitev prostorov - Eksplozivne plinske
atmosfere (IEC 60079-10-1:2015 + COR1:2015)
Explosive atmospheres - Part 10-1: Classification of areas - Explosive gas atmospheres
(IEC 60079-10-1:2015 + COR1:2015)
Explosionsgefährdete Bereiche - Teil 10-1: Einteilung der Bereiche -
Gasexplosionsgefährdete Bereiche (IEC 60079-10-1:2015 + COR1:2015)
Atmosphères explosives - Partie 10-1: Classement des emplacements - Atmosphères
explosives gazeuses (IEC 60079-10-1:2015 + COR1:2015)
Ta slovenski standard je istoveten z: EN 60079-10-1:2015
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 60079-10-1

NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2015
ICS 29.260.20 Supersedes EN 60079-10-1:2009
English Version
Explosive atmospheres - Part 10-1: Classification of areas -
Explosive gas atmospheres
(IEC 60079-10-1:2015 + COR1:2015)
Atmosphères explosives - Partie 10-1: Classement des Explosionsgefährdete Bereiche - Teil 10-1: Einteilung der
emplacements - Atmosphères explosives gazeuses Bereiche - Gasexplosionsgefährdete Bereiche
(IEC 60079-10-1:2015 + COR1:2015) (IEC 60079-10-1:2015 + COR1:2015)
This European Standard was approved by CENELEC on 2015-10-13. 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 60079-10-1:2015 E
European foreword
The text of document 31J/253/FDIS, future edition 2 of IEC 60079-10-1, 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 60079-10-1:2015.
The following dates are fixed:
• latest date by which the document has to be implemented at (dop) 2016-07-13
national level by publication of an identical national
standard or by endorsement
(dow) 2018-10-13
• latest date by which the national standards conflicting with
the document have to be withdrawn

This document supersedes EN 60079-10-1:2009.
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
1)
The text of the International Standard IEC 60079-10-1:2015 + COR1:2015 was approved by
CENELEC as a European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60079-10-2 NOTE Harmonized as EN 60079-10-2.
IEC 61285:2004 NOTE Harmonized as EN 61285:2004 (not modified).
IEC 60079-20-1 NOTE Harmonized as EN 60079-20-1.

1) COR1:2015 applies to English version only.
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 -  Explosive atmospheres - EN 60079-0 -
Part 0: Equipment - General requirements
IEC 60079-14 -  Explosive atmospheres - EN 60079-14 -
Part 14: Electrical installations design,
selection and erection
IEC 60079-10-1 ®
Edition 2.0 2015-09
INTERNATIONAL
STANDARD
colour
inside
Explosive atmospheres –
Part 10-1: Classification of areas – Explosive gas atmospheres

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.260.20 ISBN 978-2-8322-2867-8

– 2 – IEC 60079-10-1:2015 © IEC 2015
CONTENTS
FOREWORD . 6
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 General . 15
4.1 Safety principles . 15
4.2 Area classification objectives . 16
4.3 Explosion risk assessment . 16
4.4 Competence of Personnel . 17
5 Area classification methodology . 17
5.1 General . 17
5.2 Classification by sources of release method . 18
5.3 Use of industry codes and national standards . 18
5.4 Simplified methods . 18
5.5 Combination of methods . 19
6 Release of flammable substance . 19
6.1 General . 19
6.2 Sources of release . 19
6.3 Forms of release . 20
6.3.1 General . 20
6.3.2 Gaseous release . 21
6.3.3 Liquefied under pressure . 21
6.3.4 Liquefied by refrigeration . 22
6.3.5 Aerosols . 22
6.3.6 Vapours . 22
6.3.7 Liquid releases . 22
6.4 Ventilation (or air movement) and dilution . 23
6.5 Main types of ventilation . 23
6.5.1 General . 23
6.5.2 Natural ventilation. 23
6.5.3 Artificial ventilation . 24
6.5.4 Degree of dilution . 25
7 Type of zone . 26
7.1 General . 26
7.2 Influence of grade of the source of release . 26
7.3 Influence of dilution . 27
7.4 Influence of availability of ventilation . 27
8 Extent of zone . 27
9 Documentation . 28
9.1 General . 28
9.2 Drawings, data sheets and tables . 28
Annex A (informative) Suggested presentation of hazardous areas . 30
A.1 Hazardous area zones – Preferred symbols . 30
A.2 Hazardous area suggested shapes . 33

IEC 60079-10-1:2015 © IEC 2015 – 3 –
Annex B (informative) Estimation of sources of release. 35
B.1 Symbols . 35
B.2 Examples of grade of release . 35
B.2.1 General . 35
B.2.2 Sources giving a continuous grade of release . 35
B.2.3 Sources giving a primary grade of release . 36
B.2.4 Sources giving a secondary grade of release . 36
B.3 Assessment of grades of release . 36
B.4 Summation of releases . 37
B.5 Hole size and source radius . 38
B.6 Forms of release . 40
B.7 Release rate . 41
B.7.1 General . 41
B.7.2 Estimation of Release Rate . 41
B.7.3 Release rate of evaporative pools . 44
B.8 Release from openings in buildings . 46
B.8.1 General . 46
B.8.2 Openings as possible sources of release . 46
B.8.3 Openings classification . 46
Annex C (informative) Ventilation guidance . 48
C.1 Symbols . 48
C.2 General . 49
C.3 Assessment of ventilation and dilution and its influence on hazardous area . 49
C.3.1 General . 49
C.3.2 Effectiveness of ventilation . 50
C.3.3 Criteria for dilution . 50
C.3.4 Assessment of ventilation velocity . 51
C.3.5 Assessment of the degree of dilution . 52
C.3.6 Dilution in a room . 53
C.3.7 Criteria for availability of ventilation . 55
C.4 Examples of ventilation arrangements and assessments . 56
C.4.1 Introduction . 56
C.4.2 Jet release in a large building . 56
C.4.3 Jet release in a small naturally ventilated building . 57
C.4.4 Jet release in a small artificially ventilated building . 57
C.4.5 Release with low velocity . 58
C.4.6 Fugitive emissions . 59
C.4.7 Local ventilation-extraction . 59
C.5 Natural Ventilation in buildings . 60
C.5.1 General . 60
C.5.2 Wind induced ventilation . 60
C.5.3 Buoyancy induced ventilation. 61
C.5.4 Combination of the natural ventilation induced by wind and buoyancy . 63
Annex D (informative) Estimation of hazardous zones. 65
D.1 General . 65
D.2 Estimating types of the zones . 65
D.3 Estimating the extent of the hazardous zone . 65
Annex E (informative) Examples of hazardous area classification . 68

– 4 – IEC 60079-10-1:2015 © IEC 2015
E.1 General . 68
E.2 Examples . 68
E.3 Example case study for area classification . 83
Annex F (informative) Schematic approach to classification of hazardous areas . 93
F.1 Schematic approach to classification of hazardous areas . 93
F.2 Schematic approach to classification of hazardous areas . 94
F.3 Schematic approach to classification of hazardous areas . 95
F.4 Schematic approach to classification of hazardous areas . 96
Annex G (informative) Flammable mists . 97
Annex H (informative) Hydrogen . 99
Annex I (informative) Hybrid mixtures . 101
I.1 General . 101
I.2 Use of ventilation . 101
I.3 Concentration limits . 101
I.4 Chemical reactions . 101
I.5 Energy/Temperature limits . 101
I.6 Zoning requirements . 101
Annex J (informative) Useful equations in support to hazardous area classification . 102
J.1 General . 102
J.2 Dilution with air of a flammable substance release . 102
J.3 Estimate of the time required to dilute a flammable substance release . 102
Annex K (informative) Industry codes and national standards . 104
K.1 General . 104
Bibliography . 106

Figure A.1 – Preferred symbols for hazardous area zones . 30
Figure A.2 – Gas/vapour at low pressure (or at high pressure in case of unpredictable
release direction) . 33
Figure A.3 – Gas/vapour at high pressure . 33
Figure A.4 – Liquefied gas . 34
Figure A.5 – Flammable liquid (non boiling evaporative pool) . 34
Figure B.1 – Forms of release . 40
Figure B.2 – Volumetric evaporation rate of liquids . 45
Figure C.1 – Chart for assessing the degree of dilution . 52
Figure C.2 – Self diffusion of an unimpeded high velocity jet release . 57
Figure C.3 – Supply only ventilation . 58
Figure C.4 – Supply and extraction ventilation . 58
Figure C.5 – Local extraction ventilation . 60
Figure C.6 – Volumetric flow rate of fresh air per m of equivalent effective opening
area . 63
Figure C.7 – Example of opposing ventilation driving forces . 64
Figure D.1 – Chart for estimating hazardous area distances . 66
Figure E.1 – Degree of dilution (Example No. 1) . 69
Figure E.2 – Hazardous distance (Example No. 1) . 70
Figure E.3 – Zone classification (Example No. 1) . 70
Figure E.4 – Degree of dilution (Example No. 2) . 72

IEC 60079-10-1:2015 © IEC 2015 – 5 –
Figure E.5 – Hazardous distance (Example No. 2) . 73
Figure E.6 – Degree of dilution (Example No. 3) . 75
Figure E.7 – Hazardous distance (Example No. 3) . 76
Figure E.8 – Zones classification (Example No. 3) . 76
Figure E.9 – Degree of dilution (Example No. 4) . 78
Figure E.10 – Hazardous distance (Example No. 4) . 79
Figure E.11 – Zones classification (Example No. 4) . 79
Figure E.12 – Degree of dilution (Example No. 5) . 82
Figure E.13 – Hazardous distance (Example No. 5) . 83
Figure E.14 – Enclosed compressor handling natural gas . 85
Figure E.15 – Example of area classification for a compressor facility handling natural
gas (elevation) . 91
Figure E.16 – Example of area classification for a compressor facility handling natural
gas (plan) . 92
Figure F.1 – Schematic approach to classification . 93
Figure F.2 – Schematic approach to classification for continuous grade releases . 94
Figure F.3 – Schematic approach to classification for primary grade releases . 95
Figure F.4 – Schematic approach to classification for secondary grade releases . 96

Table A.1 − Hazardous area classification data sheet – Part I: Flammable substance
list and characteristics . 31
Table A.2 − Hazardous area classification data sheet − Part II: List of sources of
release . 32
Table B.1 – Suggested hole cross sections for secondary grade of releases . 39
Table B.2 – Effect of hazardous zones on openings as possible sources of release . 47
Table C.1 – Indicative outdoor ventilation velocities (u ) . 52
w
Table D.1 – Zones for grade of release and effectiveness of ventilation . 65
Table E.1 – Compressor facility handling natural gas . 86
Table E.2 – Hazardous area classification data sheet − Part I: Flammable substance
list and characteristics . 88
Table E.3 – Hazardous area classification data sheet − Part II: List of sources of
release (1 of 2) . 89
Table K.1 – Examples of codes and standards . 105

– 6 – IEC 60079-10-1:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
EXPLOSIVE ATMOSPHERES –
Part 10-1: Classification of areas –
Explosive gas 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 60079-10-1 has been prepared by subcommittee 31J:
Classification of hazardous areas and installation requirements, of IEC technical committee
31: Equipment for explosive atmospheres.
This second edition of IEC 60079-10-1 cancels and replaces the first edition, published in
2008, and constitutes a technical revision. The significant technical changes with respect to
the previous edition are as follows:

IEC 60079-10-1:2015 © IEC 2015 – 7 –
Type
Minor
Major
and
Changes Clause Extension technical
editorial
changes
changes
Complete restructuring and dividing into
sections to identify possible methodologies Main
for classifying hazardous areas and to body of X X X
provide further explanation on specific the text
assessment factors
Introducing new terms and the definitions 3 X
Introducing clauses for alternative methods
5 X X
of area classification
Updating examples for presentation of
Annex A X X
hazardous area classification
Updating calculations for release rate Annex B X X
Complete re-write with a new approach
based upon the degree of dilution instead Annex C X X
of the degree of ventilation
Introduced as a new Annex for zone

Annex D X
extents
Updated with new examples to explain the
methodology set forth in Annexes A, B, C Annex E X
and D
Update of the flow chart illustrating the
area classification procedure by dividing it Annex F X
into four sections
Introduced as a new Annex on hydrogen Annex H X
Introduced as a new Annex on hybrid
Annex I X
mixtures
Introduced as a new Annex with
Annex J X
supplementary equations
Introduced as a new Annex for reference to
national and industry codes with specific Annex K X
examples of hazardous area classification

NOTE The technical changes referred to include the significance of technical changes in the revised IEC
Standard, but they do not form an exhaustive list of all modifications from the previous version.

– 8 – IEC 60079-10-1:2015 © IEC 2015
Explanations:
Definitions
Minor and editorial changes clarification
decrease of technical requirements
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.
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 requirements.
Major technical changes addition of technical requirements
increase of technical requirements
These are changes to technical requirements (addition, increase of the level or removal).
NOTE These changes represent current technological knowledge. However, these changes should not normally
have an influence on equipment already placed on the market.
The text of this standard is based on the following documents:
FDIS Report on voting
31J/253/FDIS 31J/256/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.
A bilingual version of this publication may be issued at a later date.
The contents of the corrigendum of November 2015 have been included in this copy.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
IEC 60079-10-1:2015 © IEC 2015 – 9 –
INTRODUCTION
In areas where dangerous quantities and concentrations of flammable gas or vapour may
arise, protective measures need to be applied in order to reduce the risk of explosions. This
part of IEC 60079 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 hazards.
– 10 – IEC 60079-10-1:2015 © IEC 2015
EXPLOSIVE ATMOSPHERES –
Part 10-1: Classification of areas –
Explosive gas atmospheres
1 Scope
This part of IEC 60079 is concerned with the classification of areas where flammable gas or
vapour hazards may arise and may then be used as a basis to support the proper selection
and installation of equipment for use in hazardous areas.
It is intended to be applied where there may be an ignition hazard due to the presence of
flammable gas or vapour, mixed with air, but it does not apply to:
a) mines susceptible to firedamp;
b) the processing and manufacture of explosives;
c) catastrophic failures or rare malfunctions which are beyond the concept of abnormality
dealt with in this standard (see 3.7.3 and 3.7.4);
d) rooms used for medical purposes;
e) commercial and industrial applications where only low pressure fuel gas is used for
appliances e.g. for cooking, water heating and similar uses, where the installation is
compliant with relevant gas codes;
f) domestic premises;
g) where a hazard may arise due to the presence of combustible dusts or combustible flyings
but the principles may be used in assessment of a hybrid mixture (refer also
IEC 60079-10-2).
NOTE Additional guidance on hybrid mixtures is provided in Annex I.
Flammable mists may form or be present at the same time as flammable vapour. In such case
the strict application of the details in this standard may not be appropriate. Flammable mists
may also form when liquids not considered to be a hazard due to the high flash point are
released under pressure. In these cases the classifications and details given in this standard
do not apply. Information on flammable mists is provided in Annex G.
For the purpose of this standard, an area is a three-dimensional region or space.
Atmospheric conditions include variations 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
explosion properties of the flammable substances.
In any process plant, irrespective of size, there may be numerous sources of ignition apart
from those associated with equipment. Appropriate precautions will be necessary to ensure
safety in this context. This standard is applicable with judgement for other ignition sources.
This standard does not take into account the consequences of ignition of an explosive
atmosphere.
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

IEC 60079-10-1:2015 © IEC 2015 – 11 –
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
IEC 60079-14, Explosive atmospheres – Part 14: Electrical installations design, selection and
erection
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
explosive atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of gas,
vapour, dust, fibres, or flyings, which, after ignition, permits self-sustaining flame propagation
[SOURCE: IEC 60079-0:2013, 3.30]
3.2
explosive gas atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of gas or
vapour, which, after ignition, permits self-sustaining flame propagation
Note 1 to entry: Although a mixture which has a concentration above the upper flammable limit (UFL) is not an
explosive gas atmosphere, it can readily become so and, generally for area classification purposes, it is advisable
to consider it as an explosive gas atmosphere.
Note 2 to entry: There are some gases and vapours which are explosive with the concentration of 100 % (e.g.
acetylene, CAS no. 74-86-2, C H ; monovinyl acetylene, CAS no. 689-97-4, C H ; 1-propyl nitrate (vapour), CAS
2 2 4 4
no. 627-13-4, CH (CH ) NO ; isopropyl nitrate (vapour), CAS no. 1712-64-7, (CH ) CH ONO ; ethylene oxide
3 2 2 3 3 2 2
(vapour), CAS no. 75-21-8, (CH ) O; hydrazine (vapour), CAS no. 302-01-2, H N .
2 2 4 2
[SOURCE: IEC 60079-0:2013, 3.32, modified (addition of Notes to entry)]
3.3
hazardous areas and zones
3.3.1
hazardous area (on account of explosive gas atmospheres)
an area in which an explosive gas atmosphere is 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: The interior of many items of process equipment are commonly considered as a hazardous area
even though a flammable atmosphere may not normally be present to account for the possibility of air entering the
equipment. Where specific controls such as inerting are used the interior of process equipment may not need to be
classified as a hazardous area.
3.3.2
non-hazardous area (on account of explosive gas atmospheres)
an area in which an explosive gas atmosphere is not expected to be present in quantities
such as to require special precautions for the construction, installation and use of equipment
3.3.3
zones
hazardous area classification based upon the frequency of the occurrence and duration of an
explosive atmosphere
– 12 – IEC 60079-10-1:2015 © IEC 2015
3.3.4
zone 0
an area in which an explosive gas atmosphere is present continuously or for long periods or
frequently
Note 1 to entry: Both “long” and “frequently” are the terms which are intended to describe a very high likelihood of
a potentially explosive atmosphere in the area. In that respect, those terms do not necessarily need to be
quantified.
3.3.5
zone 1
an area in which an explosive gas atmosphere is likely to occur periodically or occasionally in
normal operation
3.3.6
zone 2
an area in which an explosive gas atmosphere is not likely to occur in normal operation but, if
it does occur, it will exist for a short period only
Note 1 to entry: Indications of the frequency of the occurrence and duration may be taken from codes relating to
specific industries or applications.
[SOURCE: IEC 60050-426:2009, 426-03-05]
3.3.7
extent of zone
distance in any direction from the source of release to where a gas/air mixture will be diluted
by air to a concentration below the lower flammable limit
3.4
releases
3.4.1
source of release
a point or location from which a flammable gas, vapour, mist or liquid may be released into
the atmosphere so that an explosive gas atmosphere could be formed
[SOURCE: IEC 60050-426:2009, 426-03-06, modified (addition of "mist")]
3.4.2
continuous grade of release
release which is continuous or is expected to occur frequently or for long periods
Note 1 to entry: Both “frequently” and “long” are the terms which are intended to describe a very high likelihood of
a potential release. In that respect, those terms do not necessarily need to be quantified.
3.4.3
primary grade of release
release which can be expected to occur periodically or occasionally during normal operation
3.4.4
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
3.4.5
release rate
quantity of flammable gas, liquid, vapour or mist emitted per unit time from the source of
release
IEC 60079-10-1:2015 © IEC 2015 – 13 –
3.5
ventilation and dilution
3.5.1
ventilation
movement of air and its replacement with fresh air due to the effects of wind, temperature
gradients, or artificial means (for example, fans or extractors)
3.5.2
dilution
the mixing of flammable vapour or gas with air which, over time, will reduce the flammable
concentration
3.5.3
dilution volume
the volume in the vicinity of a source of release where the concentration of flammable gas or
vapour is not diluted to a safe level
Note 1 to entry: In certain instances, the volumes under 3.5.3 and 3.5.5 could be the same.
3.5.4
background concentration
the mean concentration of flammable substance within the volume under consideration
outside of the release plume or jet
3.5.5
volume under consideration
the volume served by the ventilation in the vicinity of the release being considered
Note 1 to entry: For an enclosed space this could be an entire room or part of a larger space where the
considered ventilation will dilute the gas or vapour from a given source of release. Outdoors, this is the volume
around a source of release where an explosive mixture could form. In congested outdoor places this volume could
be dictated by the partial enclosure provided by the surrounding objects.
3.6
properties of flammable substance
3.6.1
flammable substance
substance which is itself flammable, or is capable of producing a flammable gas, vapour or
mist
3.6.2
flammable liquid
liquid capable of producing a flammable vapour under any foreseeable operating conditions
Note 1 to entry: An example of a foreseeable operating cond
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