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FORM FDIS (IEC)/FORMULAIRE FDIS (CEI) 2009-01-09 ® Registered trademark of the International Electrotechnical Commission 31/878/FDIS FINAL DRAFT INTERNATIONAL STANDARD PROJET FINAL DE NORME INTERNATIONALE Project number Numéro de projet IEC 60079-13 Ed. 1.0 IEC/TC or SC CEI/CE ou SC TC 31 Secretariat / Secrétariat UK Submitted for parallel voting in CENELEC Soumis au vote parallèle au CENELEC Distributed on / Diffusé le 2010-06-11 Voting terminates on / Vote clos le 2010-08-13 Also of interest to the following committees Intéresse également les comités suivants TC 18 Supersedes document Remplace le document 31/794/CDV and 31/820A/RVC Horizontal standard Norme horizontale Other TC/SCs are requested to indicate their interest, if any, in this FDIS to the TC/SC secretary Les autres CE/SC sont requis d’indiquer leur intérêt, si nécessaire, dans ce FDIS à l’intention du secrétaire du CE/SC Functions concerned Fonctions concernées Safety Sécurité EMC CEM Environment Environnement Quality assurance Assurance de la qualité CE DOCUMENT EST UN PROJET DIFFUSÉ POUR APPROBATION. IL NE PEUT ÊTRE CITÉ COMME NORME INTERNATIONALE AVANT SA PUBLICATION EN TANT QUE TELLE. OUTRE LE FAIT D'ÊTRE EXAMINÉS POUR ÉTABLIR S'ILS SONT ACCEPTABLES À DES FINS INDUSTRIELLES, TECHNOLOGIQUES ET COMMERCIALES, AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES PROJETS FINAUX DE NORMES INTERNATIONALES DOIVENT PARFOIS ÊTRE EXAMINÉS EN VUE DE LEUR POSSIBILITÉ DE DEVENIR DES NORMES POUVANT SERVIR DE RÉFÉRENCE DANS LES RÈGLEMENTATIONS NATIONALES. LES RÉCIPIENDAIRES DU PRÉSENT DOCUMENT SONT INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS, LA NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À FOURNIR UNE DOCUMENTATION EXPLICATIVE. THIS DOCUMENT IS A DRAFT DISTRIBUTED FOR APPROVAL. IT MAY NOT BE REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH. IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, FINAL DRAFT INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS. RECIPIENTS OF THIS DOCUMENT ARE INVITED TO SUBMIT, WITH THEIR COMMENTS, NOTIFICATION OF ANY RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION. Titre CEI 60079-13 Ed. 1.0: Atmosphères explosives - Partie 13: Protection du matériel par salle à surpression interne "p" Title IEC 60079-13 Ed. 1.0: Explosive atmospheres - Part 13: Equipment - protection by pressurized room "p" ATTENTION VOTE PARALLÈLE CEI – CENELEC L’attention des Comités nationaux de la CEI, membres du CENELEC, est attirée sur le fait que ce projet finale de Norme internationale est soumis au vote parallèle. Les membres du CENELEC sont invités à voter via le système de vote en ligne du CENELEC. ATTENTION IEC – CENELEC PARALLEL VOTING The attention of IEC National Committees, members of CENELEC, is drawn to the fact that this final draft International Standard (DIS) is submitted for parallel voting. The CENELEC members are invited to vote through the CENELEC online voting system. Copyright © 2010 International Electrotechnical Commission, IEC. All rights reserved. It is permitted to download this electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions. You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without permission in writing from IEC. ®

IEC 60079-13 2010 Edition - Explosive Atmospheres - Part 13

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Page 1: IEC 60079-13 2010 Edition - Explosive Atmospheres - Part 13

FORM FDIS (IEC)/FORMULAIRE FDIS (CEI) 2009-01-09 ® Registered trademark of the International Electrotechnical Commission

31/878/FDISFINAL DRAFT INTERNATIONAL STANDARD

PROJET FINAL DE NORME INTERNATIONALEProject number Numéro de projet

IEC 60079-13 Ed. 1.0

IEC/TC or SC CEI/CE ou SC TC 31

Secretariat / Secrétariat UK

Submitted for parallel voting in CENELEC Soumis au vote parallèle au CENELEC

Distributed on / Diffusé le 2010-06-11

Voting terminates on / Vote clos le 2010-08-13

Also of interest to the following committees Intéresse également les comités suivants TC 18

Supersedes document Remplace le document 31/794/CDV and 31/820A/RVC

Horizontal standard Norme horizontale

Other TC/SCs are requested to indicate their interest, if any, in this FDIS to the TC/SC secretary Les autres CE/SC sont requis d’indiquer leur intérêt, si nécessaire, dans ce FDIS à l’intention du secrétaire du CE/SC Functions concerned Fonctions concernées

Safety Sécurité

EMC CEM

Environment Environnement

Quality assurance Assurance de la qualité

CE DOCUMENT EST UN PROJET DIFFUSÉ POUR APPROBATION. IL NE PEUT ÊTRE CITÉ COMME NORME INTERNATIONALE AVANT SA PUBLICATION EN TANT QUE TELLE.

OUTRE LE FAIT D'ÊTRE EXAMINÉS POUR ÉTABLIR S'ILS SONT ACCEPTABLES À DES FINS INDUSTRIELLES, TECHNOLOGIQUES ET COMMERCIALES, AINSI QUE DU POINT DE VUE DES UTILISATEURS, LES PROJETS FINAUX DE NORMES INTERNATIONALES DOIVENT PARFOIS ÊTRE EXAMINÉS EN VUE DE LEUR POSSIBILITÉ DE DEVENIR DES NORMES POUVANT SERVIR DE RÉFÉRENCE DANS LES RÈGLEMENTATIONS NATIONALES.

LES RÉCIPIENDAIRES DU PRÉSENT DOCUMENT SONT INVITÉS À PRÉSENTER, AVEC LEURS OBSERVATIONS, LA NOTIFICATION DES DROITS DE PROPRIÉTÉ DONT ILS AURAIENT ÉVENTUELLEMENT CONNAISSANCE ET À FOURNIR UNE DOCUMENTATION EXPLICATIVE.

THIS DOCUMENT IS A DRAFT DISTRIBUTED FOR APPROVAL. IT MAY NOT BE REFERRED TO AS AN INTERNATIONAL STANDARD UNTIL PUBLISHED AS SUCH.

IN ADDITION TO THEIR EVALUATION AS BEING ACCEPTABLE FOR INDUSTRIAL, TECHNOLOGICAL, COMMERCIAL AND USER PURPOSES, FINAL DRAFT INTERNATIONAL STANDARDS MAY ON OCCASION HAVE TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL TO BECOME STANDARDS TO WHICH REFERENCE MAY BE MADE IN NATIONAL REGULATIONS.

RECIPIENTS OF THIS DOCUMENT ARE INVITED TO SUBMIT, WITH THEIR COMMENTS, NOTIFICATION OF ANY RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE AND TO PROVIDE SUPPORTING DOCUMENTATION.

Titre CEI 60079-13 Ed. 1.0: Atmosphères explosives - Partie 13: Protection du matériel par salle à surpression interne "p"

Title IEC 60079-13 Ed. 1.0: Explosive atmospheres - Part 13: Equipment - protection by pressurized room "p"

ATTENTIONVOTE PARALLÈLE

CEI – CENELEC L’attention des Comités nationaux de la CEI, membres du

CENELEC, est attirée sur le fait que ce projet finale de Norme internationale est soumis au vote parallèle.

Les membres du CENELEC sont invités à voter via le système de vote en ligne du CENELEC.

ATTENTIONIEC – CENELEC

PARALLEL VOTING The attention of IEC National Committees, members of

CENELEC, is drawn to the fact that this final draft International Standard (DIS) is submitted for parallel voting.

The CENELEC members are invited to vote through the CENELEC online voting system.

Copyright © 2010 International Electrotechnical Commission, IEC. All rights reserved. It is permitted to download this electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions. You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without permission in writing from IEC.

®

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CONTENTS

FOREWORD...........................................................................................................................5 1 Scope...............................................................................................................................7 2 Normative references .....................................................................................................10 3 Terms and definitions .....................................................................................................10 4 Requirements for rooms .................................................................................................13

4.1 General .................................................................................................................13 4.2 Construction ..........................................................................................................13 4.3 Mechanical strength ..............................................................................................14 4.4 Openings, penetrations and seals ......................................................................... 14 4.5 Doors ....................................................................................................................14 4.6 Inlets and outlets ...................................................................................................14 4.7 Ducts ....................................................................................................................14

5 Clean air supply .............................................................................................................14 5.1 Source of clean air ................................................................................................14 5.2 Environmental and air temperature conditions ....................................................... 15 5.3 Heating, ventilation and air conditioning services .................................................. 15 5.4 Minimum flow rate .................................................................................................15

6 Purging and cleaning ......................................................................................................15 6.1 General .................................................................................................................15 6.2 Gases – Purging....................................................................................................15

6.2.1 General .....................................................................................................15 6.2.2 Purge volume ............................................................................................15 6.2.3 Purging flow rate .......................................................................................15 6.2.4 Sequence of operations of the purging safety devices for type of

protection px..............................................................................................16 6.2.5 Enclosures within the room........................................................................ 16

6.3 Dusts – Cleaning ...................................................................................................16 7 Temperature limits..........................................................................................................16 8 Minimum safety provisions, safety devices and electrical disconnects ............................ 16

8.1 Safety devices.......................................................................................................16 8.2 Safety devices based upon type of protection........................................................ 17 8.3 Gas detectors ........................................................................................................18 8.4 Failure of the pressurization system ...................................................................... 18

9 Pressurized room in a hazardous area and with no internal source of flammable substance....................................................................................................................... 18 9.1 General .................................................................................................................18 9.2 Protective gas .......................................................................................................18

9.2.1 Type of protection px ................................................................................. 18 9.2.2 Type of protection py ................................................................................. 18 9.2.3 Type of protection pz ................................................................................. 19

9.3 Pressurization system ...........................................................................................19 9.3.1 Room pressure differential.........................................................................19 9.3.2 Power for pressurization system ................................................................ 19

9.4 Preventing the explosive atmosphere from entering an open door ......................... 19 9.5 Airlock ...................................................................................................................19 9.6 Outward air velocity through a door .......................................................................20

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9.7 Air consuming device ............................................................................................ 20 9.8 Action when pressurization system fails ................................................................ 20

9.8.1 Type of protection px ................................................................................. 20 9.8.2 Types of protection py and pz.................................................................... 20

9.9 Re-energizing the room .........................................................................................21 10 Pressurized room in a hazardous area and containing an internal source of

flammable substance......................................................................................................21 10.1 Evaluation of internal sources of a flammable substance ....................................... 21

10.1.1 Flammable substance assessment ............................................................21 10.1.2 Assessment of release .............................................................................. 21 10.1.3 Release – Additional requirements ............................................................21 10.1.4 Adequate dilution.......................................................................................21

10.2 Applicability of Clause 9 ........................................................................................ 21 10.3 Containment system ..............................................................................................21 10.4 Sample lines .........................................................................................................21 10.5 Types of anticipated releases ................................................................................ 22

10.5.1 General .....................................................................................................22 10.5.2 No release.................................................................................................22 10.5.3 Negligible release...................................................................................... 22 10.5.4 Limited release .......................................................................................... 22 10.5.5 Unlimited release.......................................................................................22

10.6 Safety measures ...................................................................................................23 10.7 Minimum flow rate for dilution ................................................................................23 10.8 Warning to prevent entry into a room..................................................................... 25 10.9 Air distribution .......................................................................................................25 10.10 Protective gas .......................................................................................................25 10.11 Additional pressurization system requirements when inert gas is used .................. 25

11 Pressurized room in a non-hazardous area with internal source of flammable substance (type of protection pv) .................................................................................... 25 11.1 Applicability of Clause 9 ........................................................................................ 26 11.2 Applicability of Clause 10 ...................................................................................... 26 11.3 Loss of flow of the protective gas .......................................................................... 26 11.4 Safety devices.......................................................................................................26

12 Verification ..................................................................................................................... 26 12.1 General .................................................................................................................26 12.2 Sequence of tests .................................................................................................26 12.3 Mechanical strength test........................................................................................26 12.4 Overpressure test..................................................................................................27 12.5 Purging test...........................................................................................................27 12.6 Minimum pressure differential test for types of protection px, py and pz ................ 27 12.7 Minimum flow rate test ..........................................................................................27 12.8 Overpressure test for containment systems with limited release ............................ 27 12.9 Confirmation of the ratings of the safety devices ................................................... 27 12.10 Verification sequence of operation of the safety devices........................................ 27

13 Marking .......................................................................................................................... 28 14 Technical documentation ................................................................................................28 Annex A (normative) Containment system............................................................................30 Annex B (informative) Maintenance ..................................................................................... 33

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Annex C (informative) Guidelines when pressurization not immediately restored ................. 34 Annex D (normative) Classification of the type of release within rooms ................................ 35 Bibliography.......................................................................................................................... 37 Table 1 – Exclusion of specific clauses of IEC 60079-0...........................................................8 Table 2 – Safety devices based on type of protection ........................................................... 17 Table 3 – Safety devices, loss of pressurization or use of inert protective gas ...................... 24 Table 4 – Protective gas requirements for a pressurized room with an internal flammable substance ............................................................................................................25

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INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________

EXPLOSIVE ATMOSPHERES –

Part 13: Equipment protection by pressurized room “p”

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, 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 60079-13 has been prepared by IEC technical committee 31: Equipment for explosive atmospheres.

This first edition of this part of IEC 60079 cancels and replaces the original technical report issued in 1982. It constitutes a technical revision and now has the status of an International Standard.

The significant technical changes with respect to the previous edition are listed below:

– Addition of types of protection px, py, pz and pv based upon whether external area is classified as Zone 1, Zone 2 or non-hazardous and whether internal electrical equipment is ignition capable or not.

– Addition of requirements related to Group III dusts. – Addition of equipment protection levels (EPL). – Expansion of requirements for various types of doors to prevent the entrance of a

flammable atmosphere. – Allowance for air intake located in a Zone 2 under specific conditions.

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– Addition of negligible release conditions and negligible release containment system, as well as conditions and containment for limited release and unlimited release.

This part of IEC 60079 is to be read in conjunction with IEC 60079-0.

The text of this part of IEC 60079 is based on the following documents:

FDIS Report on voting

31/XX/FDIS 31/XX/RVD

Full information on the voting for the approval of this part of IEC 60079 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.

The list of all parts of 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 date1) 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.

___________ 1) The National Committees are requested to note that for this publication the stability date is 2014.

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EXPLOSIVE ATMOSPHERES –

Part 13: Equipment protection by pressurized room “p”

1 Scope

This part of IEC 60079 gives requirements for the design, construction, assessment and testing and marking of rooms protected by pressurization in:

• a room located in an explosive gas atmosphere or explosive dust atmosphere hazardous area that does not include an internal source of a flammable substance;

• a room located in an explosive gas atmosphere or explosive dust atmosphere hazardous area that includes an internal source of a flammable substance;

• a room located in a non-hazardous area that includes an internal source of a flammable substance.

NOTE If ventilation is used and pressurization is not used, then this part of IEC 60079 does not apply. The situation is covered by the requirements of IEC 60079-10-1.

A room may be a single room, multiple rooms, a complete building or a room contained within a building and includes inlet and outlet ducts. This part of IEC 60079 also includes requirements for associated equipment, safety devices and controls necessary to ensure that pressurization is established and maintained.

This part of IEC 60079 covers rooms or buildings that are constructed or assembled on site, which may be either on land or off-shore, designed to facilitate the entry of personnel and primarily intended for installation by an end-user and verification on site. The room may be located in an explosive gas atmosphere or a explosive dust atmosphere requiring equipment protection levels (EPL) Gb, Db, Gc or Dc.

This part of IEC 60079 does not specify the methods that may be required to ensure adequate air quality for personnel with regard to toxicity and temperature within the room.

NOTE 1 Whilst the scope of this part of IEC 60079 does not address toxicity it is vital that proper consideration is given to this aspect to ensure the safety of personnel. National regulations and requirements should be observed in this regard.

NOTE 2 There is a related standard IEC60079-2 (Equipment protection by pressurized enclosure) covering the different conditions encountered when using the pressurization technique.

NOTE 3 Maintenance needs are contained in Annex B until they are included IEC 60079-17.

NOTE 4 For the purposes of this part of IEC 60079, the terms "lower flammable limit (LFL)" and "lower explosive limit (LEL)" are deemed to be synonymous, and likewise the terms "upper flammable limit (UFL)" and "upper explosive limit (UEL)" are deemed to be synonymous. For ease of reference, the two abbreviations LFL and UFL may be used hereinafter to denote these two sets of terms. It should be recognized that particular authorities having jurisdiction may have overriding requirements that dictate the use of one of these sets of terms and not the other.

This part of IEC 60079 supplements and modifies the general requirements of IEC 60079-0, except as indicated in Table 1. Where a requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of this standard takes precedence.

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Table 1 – Exclusion of specific clauses of IEC 60079-0

Clause of IEC 60079-0 Ed. 4.0 (2004)

(Informative)

Ed. 5.0 (2007)

(Informative)

Clause / subclause title

(Normative)

4 4 Equipment grouping Applies

4.1 4.1 Group I Applies

4.2 4.2 Group II Applies

4.3 4.3 Group III Applies

4.4 4.4 Equipment for a particular explosive atmosphere

Applies

5.1 5.1 Environmental influences Applies

5.1.1 5.1.1 Ambient temperature Applies

5.1.2 5.1.2 External source of heating or cooling Applies

5.2 5.2 Service temperature Applies

5.3.1 5.3.1 Determination of maximum surface temperature

Applies

5.3.2.1 5.3.2.1 Group I electrical equipment Applies

5.3.2.2 5.3.2.2 Group II electrical equipment Applies

5.3.2.3 5.3.2.3 Group III electrical equipment Applies

5.3.3 5.3.3 Small component temperature for Group I and Group II electrical equipment

Applies

6.1 6.1 General Applies

6.2 6.2 Mechanical strength Excluded

6.3 6.3 Opening times Excluded

6.4 6.4 Circulating currents Excluded

6.5 6.5 Gasket retention Excluded

6.6 6.6 Electromagnetic and ultrasonic radiating equipment

Excluded

7 7 Non-metallic enclosures and parts of enclosure

Excluded

8 8 Metallic enclosures and metallic parts of enclosures

Excluded

9 9 Fasteners Excluded

10 10 Interlocking devices Excluded

11 11 Bushings Excluded

12 12 Materials used for cementing Excluded

13 13 Ex components Excluded

14 14 Connection facilities and termination compartments

Excluded

15 15 Connection facilities for earthing and bonding conductors

Excluded

16 16 Entries into enclosures Excluded

17 17 Supplementary requirements for rotating electrical machines

Excluded

18 18 Supplementary requirements for switchgear

Excluded

19 19 Supplementary requirements for fuses Excluded

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Clause of IEC 60079-0 Ed. 4.0 (2004)

(Informative)

Ed. 5.0 (2007)

(Informative)

Clause / subclause title

(Normative)

20 20 Supplementary requirements for plugs and sockets

Excluded

21 21 Supplementary requirements for luminaires

Excluded

22 22 Supplementary requirements for caplights and handlights

Excluded

23 23 Equipment incorporating cells and batteries

Excluded

24 24 Documentation Applies

25 25 Compliance of prototype or sample with documents

Excluded

26 26 Type tests Excluded

27 27 Routine tests Applies

28 28 Manufacturers responsibility Applies

29.1 29.1 Location Applies

29.2 29.2 General Applies

NR 29.3 Ex marking for explosive gas atmospheres

Applies

NR 29.4 Ex marking for explosive dust atmospheres

Applies

29.3 29.5 Combined types of protection Applies

NR 29.6 Multiple types of protection Applies

NR 29.7 Ga using two independent Gb types of protection

Excluded

29.5 29.8 Ex components Excluded

29.6 29.9 Small equipment and small Ex components

Excluded

29.7 29.10 Extremely small equipment and extremely small Ex components

Excluded

29.8 29.11 Warning markings Applies

NR 29.12 Alternate marking of equipment protection levels (EPLs)

Applies

29.9 29.13 Cells and batteries Excluded

29.10 29.14 Examples of marking Applies

30 30 Instructions Applies

Annex A Annex A Supplementary requirements for Ex cable glands

Excluded

Annex B Annex B Requirements for Ex components Excluded

Annex C Annex C Example of rig for resistance to impact test

Applies

NR Annex D Introduction to an alternative risk assessment method encompassing “equipment protection levels” for Ex equipment

Applies

Applies – This requirement of IEC 60079-0 is applied without change.

Excluded – This requirement of IEC 60079-0 does not apply.

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Clause of IEC 60079-0 Ed. 4.0 (2004)

(Informative)

Ed. 5.0 (2007)

(Informative)

Clause / subclause title

(Normative)

NOTE The applicable requirements of IEC 60079-0 are identified by the clause title which is normative. This table was written against the specific requirements of IEC 60079-0, Ed 6.0. The clause numbers for the 6th and previous edition are shown for information only. This is to enable the General Requirements IEC 60079-0, Ed 5.0, to be used where necessary with this part of IEC 60079. Where there were no requirements for the 5th edition but there are for the 6th edition (indicated by NR against the 5th edition only), or where is a conflict between requirements, the 6th edition requirements should be considered.

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 60050(426), International Electrotechnical Vocabulary – Part 426: Equipment for explosive atmospheres

IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements

IEC 60079-2, Explosive atmospheres – Part 2: Equipment protection by pressurized enclosure “p”

IEC 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres

IEC 60695-11-10, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical flame test methods

3 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 60050(426) and IEC 60079-0 as well as the following terms and definitions apply

NOTE Unless otherwise specified, the terms “voltage” and “current” mean the r.m.s. values of an alternating, direct or composite voltage or current.

3.1 airlock means of egress, consisting of two interdependent doors designed to maintain the internal pressure of the room in order to prevent the entry of a surrounding explosive atmosphere

3.2 alarm piece of apparatus that generates a visual or audible signal that is intended to attract attention

3.3 clean air air that is essentially free of contaminants or foreign matter and contains no more than trace amounts of flammable vapour or gas

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3.4 containment system parts within the room or building containing the flammable substance that may constitute an internal source of release

NOTE The containment system may extend beyond the room or building.

3.5 dilution continuous supply of a clean air, after purging, at such a rate that the concentration of a flammable mixture inside the room is maintained at a value below the explosive limits except in a dilution area

NOTE For safety reasons, dilution to a level lower than the LEL may be required if associated with the potential release there is an additional toxic or asphyxiant risk. Further guidance can be found in IEC 61285.

3.6 dilution area area in the vicinity of a source of release where it cannot be demonstrated that the concentration of flammable gas or vapour is diluted to a safe concentration

3.7 flammable substance gases, vapours, liquids or mixtures thereof that are capable of being ignited

3.8 ignition-capable equipment ICE equipment which in normal operation constitutes a source of ignition for a specified explosive gas atmosphere

3.9 internal source of flammable substance point or location from which a flammable substance may be released into the room or building such that an explosive gas atmosphere could be formed

3.10 limited release release of flammable gas or vapour, the maximum flow rate of which can be predicted

3.11 limiting value lowest concentration value of the lower flammable limit (LFL) of each component involved, taking account of the most onerous conditions of concentration that may occur from every source of release within the room

3.12 lower flammable limit LFL volume fraction of flammable gas or vapour in air below which an explosive gas atmosphere will not form, expressed as a percentage (see IEC 60079-20-1)

NOTE This is also known as Lower Explosive Limit (LEL).

3.13 upper flammable limit UFL volume fraction of flammable gas or vapour in air above which an explosive gas atmosphere will not form, expressed as a percentage (see IEC 60079-20-1)

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NOTE This is also known as Upper Explosive Limit (UEL).

3.14 opening inlet, outlet, door or non-airtight fixed panel

3.15 pressurization technique of guarding against the ingress of the external atmosphere into a room by maintaining a protective gas therein at a pressure above that of the external atmosphere and guarding against the affects of an internal release within the room by dilution or inerting, or only guarding against the affects of an internal release within the room by dilution or inerting

NOTE Pressurization as used in this part of IEC 60079 applies to a room.

3.16 pressurization system grouping of components used to pressurize and monitor a pressurized room

3.17 pressurized room enclosed volume protected by pressurization and of sufficient size to permit the entry of a person who may be expected to work or remain inside

NOTE The term “room” is employed without distinction to designate rooms, groups of rooms or buildings.

3.18 protective gas clean air or inert gas used for purging and maintaining an overpressure and, if required, dilution

3.19 purging operation of passing a quantity of clean air through the room and ducts, so that the concentration of the explosive gas atmosphere is brought to a safe level

3.20 room volume volume of the empty room

NOTE The term “room” is employed without distinction to designate rooms, groups of rooms or buildings.

3.21 type of protection pv pressurization that reduces and maintains by adequate dilution the equipment protection level (EPL) within the pressurized room to none, where leakage from an abnormal internal source of release might occur infrequently and for a short period

3.22 type of protection px pressurization that allows for the required Gb or Db equipment protection level (EPL) within the pressurized room to be reduced to none by maintaining an internal overpressure and diluting when there is an internal source of release

3.23 type of protection py pressurization that allows for the required Gb equipment protection level (EPL) within the pressurized room to be reduced to Gc by maintaining an internal overpressure and diluting when there is an internal source of release

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3.24 type of protection pz pressurization that allows for the required Gc or Dc equipment protection level (EPL) within the pressurized room to be reduced to none by maintaining an internal overpressure and diluting when there is an internal source of release

3.25 volume fraction ratio of the volume of a component to the volume of the gas mixture under specified conditions of temperature and pressure

4 Requirements for rooms

4.1 General

This international standard addresses pressurized rooms, with the term “room” applying equally to a single room, multiple rooms or to a building, which allows for full bodily personnel access. Types of protection px, py, pz, and pv are included.

Type of protection px allows for the required Gb or Db equipment protection level (EPL) within the pressurized room to be reduced to permit the use of non-explosion protected equipment by maintaining an internal overpressure and diluting when there is an internal source of release.

NOTE 1 This permits unprotected equipment to be installed within the pressurized room except for pressurization defined safety devices (see 8.1).

NOTE 2 Because type of protection px reduces the EPL to none (a nondefined EPL) there are more onerous requirements concerning its application with respect to interlocks, alarms, etc.

Type of protection py allows for the required Gb equipment protection level (EPL) within the pressurized room to be reduced to Gc by maintaining an internal overpressure and diluting when there is an internal source of release,

NOTE 3 For pressurization defined safety devices (see 8.1).

Type of protection pz allows for the required Gc or Dc equipment protection level (EPL) within the pressurized room to be reduced to permit the use of non-explosion protected equipment by maintaining an internal overpressure and diluting when there is an internal source of release.

NOTE 4 This permits unprotected equipment to be installed within the pressurized room except for pressurization defined safety devices (see 8.1).

Type of protection pv is in essence protection by dilution, and allows for the required Gb or Gc equipment protection level (EPL) within the pressurized room to be reduced to, permit the use of non-explosion protected equipment where there is only an internal source of release and the pressurized room is located in an non-hazardous area.

4.2 Construction

The pressurized room shall, at a minimum, be designed to allow pressurization to be used in accordance with Clause 9 or Clause 10 or Clause 11.

NOTE The pressurized room construction requirements may be affected by the location, occupancy requirements, and functionality.

Dead air spaces created within the room, that may allow a gas or vapour accumulation, for example by suspended ceilings, trenches, raised floors, shall be avoided unless otherwise monitored or protected to assure that an explosive atmosphere cannot persist during normal operation.

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4.3 Mechanical strength

The room and any ducts and their connecting parts shall be designed to withstand the maximum pressure of the pressurization system. This shall be verified by the design documentation or by the overpressure test of 12.3.

The room, including windows, shall withstand the mechanical strength test of 12.3.

NOTE Test for mechanical strength need not be carried out on the completed room but may instead be applied to all parts such as windows, gland plates, penetrations, doors, inlets or outlets of the room which are not made of steel or concrete but which are integral to the type of protection. In which case the tests may be carried out on the parts themselves, appropriately mounted for the test.

4.4 Openings, penetrations and seals

The entry of cables, electrical conduits and other penetrations into the room shall be sealed so that the necessary pressure differential can be maintained.

If floor drainage facilities are provided, measures shall be taken to minimize the exchange of atmosphere between the inside and the outside of the room.

NOTE Barriers may need to be considered for certain room designs to prevent ingress of gases or vapours from potential external sources at atmospheric pressure.

4.5 Doors

All doors shall open outwards. Doors shall be automatically self closing, close fitting and designed to close and latch against the normal pressure differential.

Doors shall be capable of being opened from within, even if locked (for example by the use of a panic bar).

NOTE A second door or emergency exit remote from the first should be considered, if access to the main door may be impeded either internally or externally.

4.6 Inlets and outlets

The location of inlets and outlets shall be arranged to ensure even distribution of the clean air flow so as to avoid pockets where gases or vapours could accumulate, taking into account the density of those gases and vapours. Design parameters and constraints shall be documented.

Exterior air intakes and outlets shall be arranged to minimize the effect of outside conditions.

4.7 Ducts

Ducts for the pressurization system shall be constructed of metal or of a non-metallic material with a minimum flame resistance of V-0 according to IEC 60695-11-10.

NOTE In order to minimize the entrance of contamination into the duct, the fan suction duct should be free of leaks and protected against foreseeable mechanical damage.

5 Clean air supply

5.1 Source of clean air

The source of the clean air shall be determined from the nature of the process and the physical layout and shall be preferably from a non-hazardous area. Under certain conditions as prescribed in 9.2, the source may be from a Zone 2 hazardous area.

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5.2 Environmental and air temperature conditions

The appropriate environmental and air temperature conditions for design as determined at the inlet to the room shall be documented.

5.3 Heating, ventilation and air conditioning services

The clean air supply may include heating, ventilation, and air conditioning equipment. Any outdoor air used by heating, ventilation and air conditioning equipment shall be provided from the clean air supply.

NOTE Inlet filtering should be considered where conditions of dust, smoke, toxics or corrosive vapours or fumes may exist.

5.4 Minimum flow rate

The continuous flow of clean air through the room shall be a minimum of 5 air changes per hour. This may need to be increased for an air consuming device in accordance with 9.7 and where dilution is necessary in accordance with 10.7.

6 Purging and cleaning

6.1 General

Purging of flammable gases or removal of combustible dusts from the pressurized room is required at both the initial commissioning of the room and following loss of pressurization.

NOTE Loss of pressurization refers to complete loss of pressure differential and not a partial reduction in pressure differential.

6.2 Gases – Purging

6.2.1 General

Before energizing any electrical equipment in the pressurized room which is not suitable for the equipment protection level external to the room, it is necessary to ensure the concentration of flammable gas is less than 25 % of the limiting value (see 3.11) either by purging or by checking the atmosphere in the room with a combustible gas detector.

The pressurized room shall be purged by clean air, except where otherwise permitted or required by this part of IEC 60079.

NOTE For example, see 10.11.

6.2.2 Purge volume

The purge volume shall be a minimum of 10 room volumes unless a reduced purge volume can be verified by 12.5 or determined from criteria, such as that defined in IEC 60079-2.

6.2.3 Purging flow rate

The purging flow rate shall be a minimum of 5 air changes per hour.

The flow rate shall be monitored. Verification shall be according to 12.7.

If the room has a dedicated outlet, the flow shall be monitored at the outlet. Where there is not a dedicated outlet, gas detectors shall be used to ensure that the air within the room is at or below 25 % of the limiting value.

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6.2.4 Sequence of operations of the purging safety devices for type of protection px

The sequence of operations of the safety devices shall be as follows:

a) Following the initiation of the sequence, the purging flow through and the pressure differential between the internals of the room and the external atmosphere shall be monitored in accordance with this part of IEC 60079.

b) The purge timer shall start once the minimum specified purging flow rate through the room is verified and the pressure differential is within the specified limits.

c) When the purge time has elapsed, the purging flow rate may be reduced to the level sufficient to maintain the required positive pressure in the room. At that point, the equipment is permitted to be energised.

In the event of failure of any step in the sequence, the purging cycle shall be restarted except as specified below:

d) If the minimum specified pressure differential is not maintained and a door switch indicates that the door is not closed, the timer shall be halted until the pressure differential is re-established. If the loss of pressure differential persists for longer than 60 s the purging cycle shall be restarted regardless of the status of the door switch.

6.2.5 Enclosures within the room

During purging of the room, any enclosure which exceeds 5 % of the internal volume of the room and that contains electrical equipment not suitable for the equipment protection level external to the room, shall either be vented to the room so as to facilitate flow into and out of the enclosure or be individually purged.

NOTE Top and bottom vents providing not less than 1 cm2 of vent area for each 1 000 cm3 with a minimum vent size of 6,3 mm diameter should be sufficient for adequate purging.

6.3 Dusts – Cleaning

Before energizing any electrical equipment which is not suitable for the equipment protection level external to the room, excessive quantities of combustible dust shall be removed from the room and its contents.

7 Temperature limits

Upon failure of the pressurization system, appropriate measures shall be taken to prevent the explosive atmosphere coming into contact with any hot surface within the room that exceeds the value documented in 14.1.

NOTE This may be achieved by the design and construction of the room, (e.g. air locks) or by bringing auxiliary ventilation systems into operation or by arranging that the hot surface within the room is in a gas tight or encapsulated housing.

8 Minimum safety provisions, safety devices and electrical disconnects

8.1 Safety devices

All safety devices shall themselves be suitable for the equipment protection level external to the room or shall be mounted outside the hazardous area.

The pressurization system, its controls, electrical isolation means, the system fan and its motor shall be suitable for the area external to the room unless located in a non-hazardous area.

NOTE 1 All parts of the system in contact with the room, including inside the inlet duct should be considered as being in the hazardous area.

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The safety devices shall be used within their normal operational limits.

Alarms shall be located where they will immediately be perceived by the responsible personnel.

The safety devices required by this part of IEC 60079 form safety-related parts of a control system.

The safety and integrity of the control system shall meet a level of reliability consistent with the fault tolerance required for the relevant types of protection, i.e.

– for type of protection px, or type of protection py, a single fault; – for type of protection pz, normal operation; – for type of protection pv, single fault.

NOTE 2 For the integrity of safety functions IEC 61511 series or similar standards may be used.

Electrical power disconnection to the room should preferably be in a non-hazardous area.

8.2 Safety devices based upon type of protection

See Table 2 for required safety devices for each type of protection.

Table 2 – Safety devices based on type of protection

Design criteria Type of protection pv

Type of protection px

Type of protection py

Type of protection pz

Device to detect loss of min. pressure differential

None Pressure sensor or flow sensor (see 9.8)

Pressure sensor or flow sensor (see 9.8)

Pressure sensor or flow sensor (see 9.8)

Device to verify purge period

Time and flow marked

Timing device, pressure sensor, flow sensor (see 6.2.4)

Time and flow marked

Time and flow marked

Device for doors None Switch (see Clause 4) None None

Device for detecting loss of airflow

Flow sensor Flow sensor (see 6.2.4, 8.4)

None None

Device to detect presence of combustible gas

None Gas detector, when an airlock used without continuous flow (see 9.5)

Gas detector, when an airlock used without continuous flow (see 9.5)

Gas Detector, if air intake in Zone 2 area (see 9.2.3)

Shut down device(s)

Manual Valves to shut off flow of flammable substance

Valve to shut off an open flame (see Table 3)

Contacts to disconnect power (see Table 3)

Manual Manual

Device to permit delayed shutdown

None Optional door switch or gas detector (see 9.8.1)

None None

Device to warn against entering a room due to risk of asphyxiation or explosion

Alarm (see 8.3) Alarm (see 8.3)

Alarm (see 8.3)

Alarm (see 8.3)

None = no additional safety device required

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8.3 Gas detectors

The type, quantity and placement of detectors installed shall be based upon an end-user process risk evaluation and the specific IEC standards for gas detection (e.g. IEC 60079-29 series).

NOTE The safety requirements resulting from the risk assessment may be fulfilled by documented proven-in-use apparatus.

a) In those conditions when an asphyxiant hazard may be present, considerations shall be given towards the installation of a detection system within the room that can respond to appropriate safe gas levels in the room air with sufficient sensitivity, speed, and reliability (failure alarm, redundancy), and that can report any excursion above or below the designated concentration limit. Gas alarms shall be arranged to alarm both locally and at an attended location.

b) If the gas detector requires a specified oxygen concentration for accurate operation, then an oxygen analyzer, not subject to a common mode failure with the gas detector, is required and arranged to alarm both locally and at an attended location.

c) Any oxygen gas monitor, if used, shall be arranged to locally alarm, both audibly and visually, at 19,5 % oxygen.

8.4 Failure of the pressurization system

Failure of the pressurization system shall be determined by loss of clean air flow or by pressure differential below 25 Pa.

NOTE Unless an airlock is used, the pressure differential may be lost when a door is opened and this may result in unnecessary alarms. Detecting clean air flow does not result in these alarms.

Loss of the clean air flow shall be detected at the discharge end of the fan and shall activate an alarm locally and at an attended location.

Loss of pressure differential shall be detected by a sensor located in the room and shall activate an alarm locally and at an attended location.

9 Pressurized room in a hazardous area and with no internal source of flammable substance

9.1 General

The room shall be designed to minimize the entry of flammable gases and vapours, vapours from flammable liquids, and combustible dusts by being pressurized in accordance with types of protection px, py or pz.

9.2 Protective gas

9.2.1 Type of protection px

The clean air requirements of Clause 5 apply.

9.2.2 Type of protection py

The clean air requirements of Clause 5 apply except that the air intake may be located in a Zone 2 area using air that is essentially free of contaminants or foreign matter and contains no more than trace amounts of flammable vapour or gas under normal operating conditions.

NOTE For safety of persons working within the room, at least one combustible gas detector with alarm in the air intake is recommended.

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9.2.3 Type of protection pz

The clean air requirements of Clause 5 apply except that the air intake may be located in a Zone 2 area using air that is essentially free of contaminants or foreign matter and contains no more than trace amounts of flammable vapour or gas under normal operating conditions.

When the air intake is from a Zone 2 area, the following requirements also apply:

a) There shall be at least one combustible gas detector with alarm in the air intake. b) There shall be at least one combustible gas detector with alarm within the room. c) Gas detection in the air intake shall be arranged to shutdown the intake of air containing

flammable vapour or gas into the room on detection of 40 % of the limiting value. d) Detection and all other electrical equipment used for alarming and emergency

actions/interlocks shall have an equipment protection level of Ga or Gb.

9.3 Pressurization system

9.3.1 Room pressure differential

The pressurization system shall be capable of maintaining a pressure of at least 25 Pa in the room with all outlets open.

9.3.2 Power for pressurization system

The pressurization system shall be capable of being energized independently from the electrical power to the room.

9.4 Preventing the explosive atmosphere from entering an open door

Entry of an explosive atmosphere through an open door shall be prevented by an airlock in accordance with 9.5, or by a minimum outward velocity of air through the open door in accordance with 9.6

Exceptions are:

• doors marked “restricted access”, opened less than three times a day for no longer than 60 s each time, arranged to alarm at an attended location on being opened or not fully closed with an optional time delay of not more than 90 s and located in a Zone 2 hazardous area;

• doors used only for infrequent movement of equipment, if, under conditions of management control, these doors are marked to restrict use, are not used for egress, and are secured in the closed position;

• doors used only as emergency exits and that only open from the inside.

9.5 Airlock

Provision shall be made to ensure that the airlock either has a continuous flow of clean air equivalent to 5 volumes of the airlock per hour, or that gas detectors are installed within the airlock arranged to alarm at 25 % of the limiting value (see gas detectors in 8.3).

NOTE 1 It is the user’s responsibility to provide prompt restorative action if the gas detectors within the airlock indicate a level in excess of 25 % of the limiting value for a period of time.

Each door of the airlock shall be fitted with a device to indicate locally when the doors are not closed.

NOTE 2 An additional indication at an attended location is recommended.

Any electrical equipment within the airlock shall be suitable for the external area classification.

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Warning signs viewable upon entry or egress shall indicate that one door must be closed before the other is open (see Airlock warning in Clause 13).

9.6 Outward air velocity through a door

The minimum velocity through the door of 0.3 m/s shall be measured with all other openings capable of being opened, simultaneously open. A drop in pressure below 25 Pa is permissible during the time that these openings are open and the specified outward air velocity is maintained (see 9.3.1 and 9.4).

Openings that do not need to be considered capable of being opened include:

• doors that are specified as an exception in 9.4;

• gland or bulkhead plates or other similar covers that cannot be removed without the use of a key or tool.

NOTE The minimum outward velocity of air specified in 9.4 is based upon low wind condition and may need to be increased for local conditions.

9.7 Air consuming device

If there is an air consuming device (such as a compressor or laboratory hood) in the room, sufficient air shall be supplied to accommodate its needs as well as the needs of the pressurization system. Alternatively, the air supply to such a device shall be taken from a separate source of clean air.

9.8 Action when pressurization system fails

9.8.1 Type of protection px

Upon failure of the pressurization system, a cut-off switch shall be incorporated to de-energize power automatically from all equipment within the room not having an acceptable EPL or operation is continued under administrative controls, such as work permits. Acceptable equipment protection levels (EPL) are as follows:

• Ga or Gb for type of protection px used in an explosive gas atmosphere or;

• Da or Db for type of protection px used in an explosive dust atmosphere.

NOTE Examples of administrative controls:

1) Power to the equipment may be continued for a limited duration if loss of pressure differential has resulted from an open door.

2) Power to the equipment may be continued for a limited duration if immediate loss of power would result in a more hazardous condition and the room is equipped with gas detectors which have not exceeded 25 % of the limiting value. See gas detectors in 8.3

3) Power to the equipment may be continued for a limited duration if the area external to the room is known not to have exceeded 40% of the limiting value. Use of gas detectors may be one means of verifying this condition. See gas detectors in 8.3.

9.8.2 Types of protection py and pz

For type of protection py and type of protection pz, power to the room may be maintained upon failure of the pressurization system for a limited duration. If the pressurization system is not restored following this limited duration period, power to the room shall be de-energized to all equipment within the room not having an acceptable EPL or operation is continued under administrative controls such as work permits. Acceptable equipment protection levels (EPL) are as follows:

• Ga or Gb for type of protection py used in an explosive gas atmosphere.

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• Ga, Gb or Gc for type of protection pz used in an explosive gas atmosphere.

• Da, Db or Dc for type of protection py used in an explosive dust atmosphere.

• Da, Db or Dc for type of protection pz used in an explosive dust atmosphere.

9.9 Re-energizing the room

Provisions shall be made to energize the room safely after failure of the pressurization system. Such provisions include removing combustible dust by cleaning in accordance with 6.3 or for explosive gases, either purging in accordance with 6.2 or measuring the atmosphere in the room with a combustible gas detector to ensure the concentration of flammable gas is less than 25 % of the limiting value.

10 Pressurized room in a hazardous area and containing an internal source of flammable substance

NOTE Examples include an analyzer room, a metering station and a quality laboratory.

10.1 Evaluation of internal sources of a flammable substance

10.1.1 Flammable substance assessment

Perform an assessment to determine the following:

• the chemical and physical properties of the flammable substances,

• the processing conditions of the flammable substances,

• the potential for releasing the flammable substances within the room including flow restriction devices, such as external orifices, and the general room design.

10.1.2 Assessment of release

Determine the anticipated release for each flammable substance for both normal and abnormal release based upon the assessment.

10.1.3 Release – Additional requirements

Apply the additional requirements for the anticipated releases as described in Table 3.

10.1.4 Adequate dilution

Modify the minimum flow rate required for pressurization if necessary for adequate dilution, see 10.7.

10.2 Applicability of Clause 9

All the requirements of Clause 9 apply.

10.3 Containment system

Each internal source of a flammable substance shall be contained in accordance with Annex A.

10.4 Sample lines

To allow flushing of affected equipment before performing maintenance, clean-out connections shall be provided in sample lines at appropriate locations.

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10.5 Types of anticipated releases

10.5.1 General

Every room containing a source of flammable substance shall be considered to have one of the following types of anticipated releases.

NOTE The type of the anticipated release is defined by the requirements which characterize that release.

The determination of whether leakage is likely or not likely to occur shall be based on the most onerous conditions of service.

10.5.2 No release

There is no internal release when the containment system is infallible, see Clause A.2.

NOTE The containment system should be composed of metallic, ceramic or glass, pipes, tubes or vessels which have no moving joints. Joints should be made by welding, brazing, glass to metal sealing, or by eutectic methods.

10.5.3 Negligible release

Since it is required to have a minimum flow rate of 5 air changes per hour, minor releases of a flammable substance because of the construction of the containment system, or release of a flammable substance that is already diluted is acceptable. The following are considered as having negligible release:

a) a containment system with a negligible release, as given in A.2.3; b) flammable substances inside the containment system are in the gas or vapour phase when

operating between the specified temperature limits and either: 1) the gas mixture within the containment system is always below 25% of the limiting

value; or 2) the minimum pressure specified for the pressurized room is at least 50 Pa higher than

the maximum pressure specified for the containment system and an automatic safety device is provided to operate if the pressure difference falls below 50 Pa.

10.5.4 Limited release

The rate of release is limited when the release of a flammable substance into the pressurized room is any of the following:

a) predictable in all conditions of containment system failure, see Annex A; b) limited as in item a) above, but the conversion of the liquid into a flammable vapour is not

predictable, see Annex D; c) limited as in item b) above and if oxygen may be released from the liquid, the maximum

flow rate of oxygen shall be predictable to be less than 2 % volume fraction, see Annex A; d) limited to an amount that can be diluted by the pressurization system to a concentration

less than 25 % of the lower flammable limit.

To prevent an unlimited release in the room, process streams shall have orifices or other flow-limiting devices on the inlets and on the outlet, if the outlet can constitute a source of uncontrolled leakage from the process. Orifices or other flow-limiting devices shall be located outside and close to the wall of the room.

10.5.5 Unlimited release

The rate of release is unlimited when the release of the flammable substance is of such a magnitude that it cannot be diluted by the pressurization system to a concentration less than 25 % of the lower flammable limit.

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10.6 Safety measures

The safety measures contained in Table 3 are required when there is either an internal release or when the protective gas is inert.

10.7 Minimum flow rate for dilution

Annex B of IEC 60079-10-1 provides guidance on determining the required air flow rates for suitably diluting sources of release.

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Table 3 – Safety devices, loss of pressurization or use of inert protective gas

Type of Release Requirement

No release

Based upon infallible containment

There are no additional requirements beyond those in Clause 9.

Negligible release

Based upon negligible release containment

There are no additional requirements beyond those in Clause 9, based upon a minimum protective gas flow rate of 5 air changes per hour.

Negligible release

Based upon flammable substance does not exceed 25 % Limiting value

There are no additional requirements beyond those in Clause 9, based upon a minimum protective gas flow rate of 5 air changes per hour.

Negligible release

Based upon room pressure being at least 50 Pa higher than maximum process pressure of the flammable substance within the containment system

In addition to the requirements in Clause 9, in the event differential pressure 50 Pa higher than the process pressure is not maintained:

a) An audible and visual alarm shall be activated at a constantly attended location.

b) Electrical power to ignition-capable equipment within the room shall be automatically shut down; however, power to the circuits shall be permitted to be continued for a short period if immediate loss of power or automatic shutdown would result in a more hazardous condition and the room is equipped with gas detectors which have not exceeded 25 % of the limiting value. See gas detectors in 8.3.

c) Open flames shall be automatically extinguished.

d) Power shall not be restored until the room is below ignitable concentration of the flammable substance.

e) Provide alarms to warn against entry into the room or to indicate to leave the room in accordance with 10.8

Limited release

Based upon providing adequate flow to dilute to less than 25% LEL

In addition to the requirements in Clause 9, the protective gas must be determined in accordance with Table 4 and in the event of loss of flow, the following shall be required:

a) An audible and visual alarm shall be activated at a constantly attended location.

b) Electrical power to ignition-capable equipment within the room shall be automatically shut down; however, power to the circuits shall be permitted to be continued for a short period if immediate loss of power or automatic shutdown would result in a more hazardous condition and the room is equipped with gas detectors which have not exceeded 25 % of the limiting value. See gas detectors in 8.3.

c) Open flames shall be automatically extinguished.

d) Power shall not be restored until the room is below ignitable concentration of the flammable substance.

e) Provide alarms to warn against entry into the room or indicate to leave the room in accordance with 10.8.

f) Automatically isolate sample and utility streams

Unlimited release In addition to the requirements in Clause 9, the protective gas must be inert and in the event of failure of the pressurization system:

a) An audible and visual alarm shall be activated at a constantly attended location.

b) Electrical power to ignition-capable equipment within the room shall be automatically shut down.

c) Power shall not be restored until the oxygen concentration in the room is less than 2 % volume fraction.

d) Automatically isolate sample and utility streams

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10.8 Warning to prevent entry into a room

A room where loss of pressurization could contribute either to a build-up of flammable gases or vapours or where the protective gas is inert shall incorporate safety devices arranged to audibly and visually alarm to warn personnel against entering the room due to the existence of either or both of these conditions. Alarms shall also be audible inside the room. The room shall be marked in accordance with Clause 13. This alarm will also provide warning to personnel to leave the room.

10.9 Air distribution

Flow of air through the room shall ensure adequate air distribution. Flammable vapours shall be removed as close to their source as practical.

10.10 Protective gas

The choice of protective gas depends upon the probability, quantity and constituents of the release from the containment system. See Table 4 for tabulation of the permitted protective gas.

Table 4 – Protective gasa requirements for a pressurized room with an internal flammable substance

Internal release (see Annex A and Annex D) Continuous dilution

Substance Normal Abnormal UFL < 80 % UFL > 80 %

Gas or liquid None None Not applicable

Gas None Limited Air or inert Air

Gas Limited Limited Air or inert Air

Liquid None Limited Inert only <no>

Liquid Limited Limited <no> <no>

<no> indicates that pressurization is not suitable.

a The protective gas shall preferably be air.

Inert gas, such as nitrogen, which is a known asphyxiant, may be used only as specified in 10.11 below.

10.11 Additional pressurization system requirements when inert gas is used

Inert gas used for purging or pressurization in a room depletes the room’s oxygen. The room shall be equipped with an oxygen monitor in accordance with 8.3 c).

Where personnel can enter the room, administrative controls combined with adequate training and safe entry procedures shall be established. Warning signs advising of the hazard of inert gas shall be posted in accordance with Clause 13.

Inert gas shall not be used for purging an entire room where personnel are permitted to enter without administrative controls.

11 Pressurized room in a non-hazardous area with internal source of flammable substance (type of protection pv)

NOTE Examples include an analyzer room, a metering station and a quality laboratory.

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11.1 Applicability of Clause 9

All the requirements of Clause 9 apply to this section except for retaining the 25 Pa pressure differential (9.3.1) and preventing the entry of the external atmosphere (9.4, 9.5, 9.6)

11.2 Applicability of Clause 10

The requirements of 10.3 to 10.5 apply to Clause 11.

11.3 Loss of flow of the protective gas

Loss of protective gas flow shall be detected and shall activate an alarm locally and at an attended location.

11.4 Safety devices

The pressurization system, its controls, electrical isolating means and system fan and its motor located inside the room shall be suitable for the conditions for release internally in the room. Where located outdoors, these shall be suitable for the environmental conditions.

12 Verification

12.1 General

An assessment and test report documenting the safety aspects of the pressurized room and the findings of this verification process shall be retained in the technical documentation.

Tests judged to be unnecessary may be omitted provided justification for the omission(s) is included in the technical documentation.

12.2 Sequence of tests

The room shall be subjected to the following tests as applicable and in the following sequence:

• mechanical strength test;

• overpressure test;

• purging test;

• minimum pressure differential test;

• minimum flow rate test;

• overpressure test for containment systems with limited release;

• verification of sequence of operation of the safety devices.

12.3 Mechanical strength test

Where design records for the room are not available, then parts of the room most likely to be damaged so as to reduce the pressure differential below the minimum required shall be submitted to a mechanical strength test consisting of an impact from a hardened steel 1 kg test mass in the form of a hemisphere of 25 mm diameter dropped from a height of 1 m.

The mechanical strength test shall not produce damage so as to reduce the pressure differential below the minimum required.

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12.4 Overpressure test

A pressure equal to the maximum pressure that can be achieved by the pressurization system shall be applied to the room and associated ducts and their connecting parts where they are an integral part of the room.

The test shall be applied for a period of 5 min ± 60s.

The test is satisfactory if no permanent deformation occurs which would invalidate the type of protection.

12.5 Purging test

The room shall be visibly filled with chemical smoke. As soon as the room is filled the smoke supply shall be turned off and the clean air supply turned on at the minimum purging rate. By the completion of the specified purging time, all visible smoke shall have been removed from the room.

NOTE The room does not have to be completely filled with smoke at one time, but smoke may be added to locations sequentially to determine if there are poorly ventilated spaces.

12.6 Minimum pressure differential test for types of protection px, py and pz

A test shall be made to verify that the pressurization system is capable of maintaining a minimum pressure differential of 25 Pa with 100 % of the outlets open at the minimum pressurization flow rate.

12.7 Minimum flow rate test

A test shall be made to verify that the pressurization system is capable of maintaining the minimum flow rate required with 50 % of the outlets closed.

12.8 Overpressure test for containment systems with limited release

A test pressure of at least 1,5 times the maximum rated pressure specified for normal service shall be applied to the containment system and maintained for a period of 2 min ± 10 s. The test pressure shall have a minimum value not less than 200 Pa, where the contents of the containment system are always completely in the gas or vapour phase, or 400 kPa otherwise.

NOTE Liquid samples require a minimum static of at least 10 kPa to ensure flow. Normal values will lie in the range 100 kPa to 20 MPa or higher. Static head does not account for expected impulse conditions or resonance effects. The level of 400 kPa has been chosen to verify a minimum level of integrity that might be expected of a liquid containment system without being unduly onerous.

The test is satisfactory if no permanent deformation occurs which would invalidate the containment.

12.9 Confirmation of the ratings of the safety devices

Safety devices shall have an EPL acceptable for the location.

The ratings of the components used in the containment system shall be verified for pressure ratings compatible with actual pressures to be encountered. For containment systems with a limited release, the pressure rating can alternately be verified by the test of 12.8.

12.10 Verification sequence of operation of the safety devices

The sequence of operation of the safety devices as specified shall be verified to be in accordance with 6.2.4. The test shall be conducted at the rated nominal supply voltage, frequency and temperature.

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13 Marking

Markings using equivalent text may be used.

The isolating switch shall be clearly marked:

“WARNING – Run fan for T min before energizing the installation, unless the atmosphere inside the room is known not to be hazardous.”

Where T is the minimum specified time to purge the room.

All doors to the pressurized room shall be clearly marked on the inside and the outside, by the following:

“WARNING – Pressurized room – Keep door closed”

Each infrequently used entrance to a room in a zone 2 area shall be marked to restrict access such as with the following:

“AUTHORIZED PERSONNEL ONLY”

An airlock shall be clearly marked with the following:

“WARNING – Verify other door is closed before opening this door”

Each entrance to a room where the protective gas is inert shall be clearly marked with the following:

“DANGER – Room does not contain breathable air and is an asphyxiation hazard”

Each entrance to a room where loss of pressurization could result in an alarm indicating an asphyxiation hazard from build-up of inert gas shall be clearly marked with the following:

“DANGER – Do not enter when alarm sounds. Room does not contain breathable air and is an asphyxiation hazard”

Each entrance to a room where loss of pressurization could result in an alarm indicating an explosion hazard from build-up of flammable gas or vapours shall be clearly marked with the following:

“DANGER – Do not enter when alarm sounds, room contains a dangerous level of combustible gas and is an explosion hazard”

14 Technical documentation

In addition to that required by IEC 60079-0, the documentation shall also include the following:

• the internal volume of the room including the volume of the ducts,

• the maximum surface temperature of equipment within the room, when type of protection py pressurization is used,

• minimum quantity of clean air required for purging,

• minimum purging flow rate,

• minimum purging duration,

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• the point or points at which the pressure is to be monitored,

• location of the air intakes, and outlets, when outlets are used. For example, documentation shall identify whether the location of the air intake is in a Zone 2 location,

• range of temperatures for the clean air at the inlets to the room when outside of normal temperature range, see 5.2,

• permitted range of operating temperature within the room when outside of normal temperature range,

• purge gas, if other than air,

• information regarding any internal or external equipment intended to remain energized when the pressurization or ventilation system is not active,

• gas detection as applicable.

In addition to the above, any room with a containment system shall be documented with the following:

• maximum flow rate into the containment system;

• maximum oxygen concentration in the containment system;

• maximum rated pressure of the containment system.

For type of protection px, a functional sequence diagram shall be provided, for example a truth table, state diagram, flow chart, etc., to define the action of the control system. The sequence diagram shall clearly identify and show the operational states of the safety devices and ensuing actions. Functional tests shall be conducted to verify conformity to the diagram, see 12.9. The diagram should include:

• purging cycle,

• delays programmed in if pressure differential device trips, but door is detected to be open,

• delays programmed in if pressure differential device trips, but gas detector shows no hazardous atmosphere.

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Annex A (normative)

Containment system

A.1 General

Flammable gases or vapour mixtures that are within the flammable range that are piped to the room shall have suitable means to prevent propagation of an explosion back to the source.

Means for emergency isolation of the process shall be provided outside the room.

If there is more than one containment system with no shared connection, each shall be assessed separately.

The maximum operating pressure and the flow rate into the containment system in normal service shall be established. Where the containment system comprises several components, the rated design pressure of the containment system shall not exceed the manufacturer’s rated pressure of any component of the containment system with a safety factor of 1,5.

Details of the constructional design of the containment system, the types and operating conditions of flammable substances it may contain and the expected release rate or rates at given locations, shall be documented.

The containment system may be comprised of parts or components that are infallible or with limited release as shown in Clause A.2.

A.2 Design requirements for the containment system

A.2.1 General design requirements

The design and construction of the containment system, which will determine whether leakage is likely to occur or not, shall be based on the most onerous conditions of service specified.

The containment system shall be either infallible or have a limited release upon failure. If the flammable substance is a liquid, there shall be no normal release (see A.2.3) and the protective gas shall be inert.

NOTE The protective gas needs to be inert to prevent the vapours from the process from exceeding the capabilities of the diluting protective gas.

The maximum inlet pressure to the containment system shall be specified.

Details of the design and construction of the containment system, the types and operating conditions of the flammable substance it may contain and the expected release rate or rates at given locations, shall be provided in order for the containment system to be classified as an infallible containment system (A.2.2.) or a containment system with negligible release (A.2.3) or a containment system with limited release (A.2.4).

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A.2.2 Infallible containment system

The containment system shall be composed of metallic, ceramic or glass pipes, tubes or vessels which have no moving joints. Joints shall be made by welding, brazing, glass to metal sealing, or by eutectic methods2.

Low temperature solder alloys such as lead/tin composites are not acceptable.

NOTE Damage to a potentially fragile containment system by adverse operating conditions should be taken into consideration. Adverse operating conditions may include vibration, thermal shock and maintenance operations when doors or access covers of the room are open.

A.2.3 Containment system with a negligible release

The containment system shall be constructed as an infallible containment system, but may also include the following:

– tightly anchored pipes of proper material, – flanged connections or compression couplings, – compression fittings with front and back ferrules , – elastic seals of tongue and groove construction, – flow meters with all metal housings, – bellow seals (limited life has to be taken into account).

A.2.4 Containment system with a limited release

The design of a containment system with limited release shall be such that the rate of release of the flammable substance is predictable in all conditions of containment system failure. The quantity of flammable substance released into the room includes the quantity of flammable substance in the containment system and the flow of the flammable substance entering the containment system from the process. The flow shall be limited to a predictable rate by appropriate flow limiting devices fitted outside the room.

However, if that part of the containment system from the entry point into the room up to and including the inlet to the flow limiting device conforms to A.2.2, the flow limiting device may be installed inside the room, in which case the flow limiting device shall be permanently secured and shall have no movable parts.

The process flow into the containment system need not be limited if the maximum release rate from the containment system into the room can be predicted. This condition can be met when

a) the containment system comprises connected parts which individually meet the requirements of A.2.2 and the joints between the parts are so constructed that the maximum release rate can be predicted and the joints are permanently secured or

b) the containment system includes orifices, or nozzles for the purpose of release in normal operation (for example, flames) but otherwise meets the requirements of A.2.2.

If the flow limiting device is not included as part of the equipment, specific information regarding flow-limiting devices, including the maximum pressure and flow of the flammable substance into the containment system, shall be in the technical documentation.

Rooms containing a flame shall be assessed as though the flame had been extinguished. The maximum quantity of the fuel/air mixture which supplies the flame shall be added to the quantity of release from the containment system.

___________ 2 A method of joining two or more components, normally metallic, employing a binary or ternary alloy system

which solidifies at a constant temperature which is lower than the beginning of solidification of any of the components being joined.

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NOTE 1 Elastomeric seals, windows and other non-metallic parts of the containment system are permissible. Pipe threads, compression joints (for example, metallic compression fittings), and flanged joints are also permissible.

NOTE 2 Consideration should be given by the user to the possible formation of a flammable mixture due to the possibility of air penetration into the containment system and the resulting additional precautions that may be necessary.

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Annex B (informative)

Maintenance

B.1 Periodic verification

In addition to the activities required by IEC 60079-17, the following should be verified on a periodic basis:

• performance of safety devices,

• integrity of ducting,

• integrity of penetrations,

• integrity of containment system (especially plastic tubing),

• flammable substances being used are permitted by technical documentation,

• documentation required in Clause 14 for safe shut down and start-up is still appropriate,

• training instructions.

B.2 Modifications

Modification to the room and its contents (e.g. flammable substance, electrical equipment, safety device, etc.) must be assessed and documented that it does not compromise the type of protection.

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Annex C (informative)

Guidelines when pressurization not immediately restored

Buildings will sometimes contain equipment and circuits which due to their criticality of operation must remain in service even in the presence of failed pressurization. Some acts and regulations even recognize that it is preferable to maintain an energized circuit where it can be demonstrated that to de-energise and shut down would lead to a more unsafe condition. Additional layers of protection may be required by the room equipment, especially for circuits whose nature of application and operation, may require being energized at all times. Examples included but are not limited to ventilation, purging and pressurization equipment fans, door switches, fire and gas detection systems and essential plant controls.

Additional protective measures will be required such as demonstrable energy limitation to ensure circuits remain non-incendive or even the application of equipment protection by pressurization of enclosures within rooms or buildings. As an example, a concrete constructed substation containing electrical switch gear and control panels may be protected by both pressurizing the room and by separately pressurizing the switch gear enclosures in accordance with IEC 60079-2. These two pressurized protection applications must be completely independent of one another.

‘As Low As Reasonably Practicable (ALARP)’ principles and the probability of simultaneous faults and failures, should be borne in mind, so the levels of protection required to properly manage the risk can be applied.

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Annex D (normative)

Classification of the type of release within rooms

D.1 General

The consequences of a release of flammable substances within a room are more severe than a similar release in free air. A temporary leak inside a room will build up flammable substances which will remain inside the room for a long time even after the leak stops.

Because of this, it is necessary to assign greater importance to “normal release” and “abnormal release” than for a release in open air.

In all cases, devices shall be fitted to limit the flow of flammable substances from the containment system into the room.

D.2 No normal release, no abnormal release

A containment system which meets the design requirements in A.2.2 shall be considered to have no normal release and no abnormal release.

D.3 No normal release, limited abnormal release

A containment system which does not meet the requirements for infallible containment and comprises metallic pipes, tubes or elements such as Bourdon tubes, bellows or spirals, with joints not subject to disconnection during routine maintenance and made with pipe threads, welding, eutectic methods, or metallic compression fittings shall be considered to have no normal release but limited abnormal release.

Rotating or sliding joints, flanged joints, elastomeric seals and non-metallic flexible tubing do not satisfy the criteria for limited abnormal release.

D.4 Limited normal release

Systems which cannot meet the requirements for "no normal release" shall be considered to have a limited normal release. This includes containment systems with joints subject to routine maintenance. Such joints shall be clearly identified.

Containment systems whose construction comprises non-metallic pipes, tubes, or elements such as Bourdon tubes, bellows, diaphragms, spirals, elastomeric seals, rotating or sliding joints shall be considered to be a source of release in normal operation.

Equipment having a flame in normal operation shall be assessed with the flame extinguished.

It shall be assumed that extinguishing of the flame is a normal occurrence and that the equipment shall be classified as having a normal release unless devices are fitted to stop the flow of flammable gas or vapour automatically upon flame extinction.

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D.5 Unlimited release

Systems which cannot meet requirements for “limited normal release” shall be considered to have unlimited release. Joints in “unlimited release” piping systems are not specified.

Only inert gas is permitted as pressurizing medium where unlimited release is identified. Pressurizing with inert gas requires reducing the oxygen content in the room to less than 2 % by volume.

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Bibliography

IEC 60050(151), International Electrotechnical Vocabulary – Part 151: Electrical and magnetic devices

IEC 60079-17, Explosive atmospheres – Part 17: Electrical installations inspection and maintenance

IEC 60079-20-1, Explosive atmospheres – Part 20-1: Material characteristics for gas and vapour classification – Test methods and data

IEC 60079-29 (all parts), Explosive atmospheres – Gas detectors

IEC 60529, Degrees of protection provided by enclosures (IP Code)

IEC 61285, Industrial-process control – Safety of analyzer houses

IEC 61511 (all parts), Functional safety – Safety instrumented systems for the process industry sector

IEC/TR 61831, On-line analyser systems – Guide to design and installation

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