Bsi bs en 60079 13 2010

BS EN 60079-13:2010 BSI Standards Publication Explosive atmospheres Part 13: Equipment protection by pressurized room “p” BRITISH STANDARD BS EN 60079-13:2010 National foreword This British Standard is the UK implementation of EN 60079-13:2010 It is identical to IEC 60079-13:2010 The UK participation in its preparation was entrusted by Technical Committee GEL/31, British Electrotechnical Committee, to Subcommittee GEL/31/X, Equipment for explosive atmospheres A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © BSI 2011 ISBN 978 580 60924 ICS 29.260.20 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 May 2011 Amendments issued since publication Amd No Date Text affected BS EN 60079-13:2010 EUROPEAN STANDARD EN 60079-13 NORME EUROPÉENNE December 2010 EUROPÄISCHE NORM ICS 29.260.20 English version Explosive atmospheres Part 13: Equipment protection by pressurized room "p" (IEC 60079-13:2010) Atmosphères explosives Partie 13: Protection du matériel par salle surpression interne "p" (CEI 60079-13:2010) Explosionsfähige Atmosphäre Teil 13: Geräteschutz durch überdruckgekapselte Räume (IEC 60079-13:2010) This European Standard was approved by CENELEC on 2010-12-01 CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CENELEC member This European Standard exists in three official versions (English, French, German) A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung Management Centre: Avenue Marnix 17, B - 1000 Brussels © 2010 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members Ref No EN 60079-13:2010 E BS EN 60079-13:2010 EN 60079-13:2010 -2- Foreword The text of document 31/878/FDIS, future edition of IEC 60079-13, prepared by IEC TC 31, Equipment for explosive atmospheres, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 60079-13 on 2010-12-01 This part of EN 60079 is to be read in conjunction with EN 60079-0 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CEN and CENELEC shall not be held responsible for identifying any or all such patent rights The following dates were fixed: – latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2011-09-01 – latest date by which the national standards conflicting with the EN have to be withdrawn (dow) 2013-12-01 Annex ZA has been added by CENELEC Endorsement notice The text of the International Standard IEC 60079-13:2010 was approved by CENELEC as a European Standard without any modification In the official version, for Bibliography, the following notes have to be added for the standards indicated: IEC 60079-17 NOTE Harmonized as EN 60079-17 IEC 60079-20-1 NOTE Harmonized as EN 60079-20-1 IEC 60079-29 series NOTE Harmonized in EN 60079-29 series (partially modified) IEC 60529 NOTE Harmonized as EN 60529 IEC 61285 NOTE Harmonized as EN 61285 IEC 61511 series NOTE Harmonized in EN 61511 series (not modified) BS EN 60079-13:2010 EN 60079-13:2010 -3- Annex ZA (normative) Normative references to international publications with their corresponding European publications 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 NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies Publication Year Title EN/HD Year IEC 60050-426 - International Electrotechnical Vocabulary Part 426: Equipment for explosive atmospheres - - IEC 60079-0 - Explosive atmospheres Part 0: Equipment - General requirements EN 60079-0 - IEC 60079-2 - Explosive atmospheres Part 2: Equipment protection by pressurized enclosure "p" EN 60079-2 - IEC 60079-10-1 - EN 60079-10-1 Explosive atmospheres Part 10-1: Classification of areas - Explosive gas atmospheres - IEC 60695-11-10 - Fire hazard testing EN 60695-11-10 Part 11-10: Test flames - 50 W horizontal and vertical flame test methods - BS EN 60079-13:2010 –2– 60079-13 © IEC:2010 CONTENTS Scope .7 Normative references 10 Terms and definitions 10 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 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 Purging and cleaning 15 6.1 6.2 General 15 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 Temperature limits 16 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 Pressurized room in a hazardous area and with no internal source of flammable substance 18 9.1 9.2 9.3 9.4 9.5 9.6 General 18 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 Pressurization system 19 9.3.1 Room pressure differential 19 9.3.2 Power for pressurization system 19 Preventing the explosive atmosphere from entering an open door 19 Airlock 19 Outward air velocity through a door 20 BS EN 60079-13:2010 60079-13 © IEC:2010 –3– 9.7 9.8 Air consuming device 20 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 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 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 BS EN 60079-13:2010 –4– 60079-13 © IEC:2010 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 – Exclusion of specific clauses of IEC 60079-0 Table – Safety devices based on type of protection 17 Table – Safety devices, loss of pressurization or use of inert protective gas 24 Table – Protective gas requirements for a pressurized room with an internal flammable substance 25 BS EN 60079-13:2010 60079-13 © IEC:2010 –7– EXPLOSIVE ATMOSPHERES – Part 13: Equipment protection by pressurized room “p” 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 situation is covered by the requirements of IEC 60079-10-1 The 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 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 There is a related standard IEC60079-2 (Equipment protection by pressurized enclosure) covering the different conditions encountered when using the pressurization technique NOTE Maintenance needs are contained in Annex B until they are included IEC 60079-17 NOTE 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 Where a requirement of this standard conflicts with a requirement of IEC 60079-0, the requirement of this standard takes precedence BS EN 60079-13:2010 –8– 60079-13 © IEC:2010 Table – Exclusion of specific clauses of IEC 60079-0 Clause of IEC 60079-0 Ed 4.0 (2004) (Informative) Ed 5.0 (2007) (Informative) 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 Clause / subclause title (Normative) 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 Non-metallic enclosures and parts of enclosure Excluded 8 Metallic enclosures and metallic parts of enclosures Excluded 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 BS EN 60079-13:2010 – 26 – 11.1 60079-13 © IEC:2010 Applicability of Clause All the requirements of Clause 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 kg test mass in the form of a hemisphere of 25 mm diameter dropped from a height of m The mechanical strength test shall not produce damage so as to reduce the pressure differential below the minimum required BS EN 60079-13:2010 60079-13 © IEC:2010 12.4 – 27 – 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 ± 60 s 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 ± 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 BS EN 60079-13:2010 – 28 – 60079-13 © IEC:2010 13 Marking Markings using equivalent text may be used The isolating switch shall be clearly marked: “WARNING – Run fan for T 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 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, BS EN 60079-13:2010 60079-13 â IEC:2010 29 ã 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 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 BS EN 60079-13:2010 – 30 – 60079-13 © IEC:2010 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 A.2.1 Design requirements for the containment system 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) BS EN 60079-13:2010 60079-13 © IEC:2010 A.2.2 – 31 – 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 methods 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 _ 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 BS EN 60079-13:2010 – 32 – 60079-13 © IEC:2010 NOTE 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 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 BS EN 60079-13:2010 60079-13 © IEC:2010 – 33 – 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 BS EN 60079-13:2010 – 34 – 60079-13 © IEC:2010 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 BS EN 60079-13:2010 60079-13 © IEC:2010 – 35 – 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 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 BS EN 60079-13:2010 – 36 – D.5 60079-13 © IEC:2010 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 % by volume BS EN 60079-13:2010 60079-13 © IEC:2010 – 37 – 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 This page deliberately left blank This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other standards-related publications, information and services BSI is incorporated by Royal Charter British Standards and other standardization products are published by 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