Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours

The standard test method is designed to determine the explosion pressure and the maximum explosion pressure of a flammable gas/air/inert mixture at ambient temperature and pressure.
The standard test method is designed to produce measurements of the rate of explosion pressure rise and the maximum rate of explosion pressure rise of a flammable gas/air/inert mixture in a closed volume at ambient temperature and pressure.
In this European Standard, the term "gas" includes vapours but not mists. Detonation and decomposition phenomena are not considered in this European Standard.

Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen zeitlichen Druckanstieges für Gase und Dämpfe

Diese Europäische Norm legt ein Verfahren zur Bestimmung des Explosionsdrucks und des maximalen Explosionsdrucks sowie des zeitlichen Explosionsdruckanstieges und des maximalen zeitlichen Explosionsdruckanstieges eines ruhenden Gemischs aus brennbarem Gas (Brennstoff), Luft und Inertgas bei Umgebungsbedingungen in geschlossenen Behältern ohne Einbauten fest. In dieser Europäischen Norm schließt der Begriff „Gas“ auch Dämpfe, jedoch keine Nebel, ein. Diese Europäische Norm gilt nicht für Bedingungen, unter denen Detonations- und Zersetzungsphänomene auftreten können. Die nach den in der vorliegenden Europäischen Norm festgelegten Verfahren gemessenen Drücke und zeitlichen Druckanstiege sind für die Auslegung von druckfesten Kapselungen, das sind Umschließungen, die konstruktiv so ausgelegt sind, dass sie einer im Innern stattfindenden Explosion standhalten und diese nicht in eine äußere explosionsfähige Atmosphäre übertragen, oder anderen geschlossenen Behältern, deren innere Geometrie zu einer Drucküberhöhung führen kann, nicht anwendbar. Selbst in einer Umschließung von relativ einfacher Geometrie können Einbauten zu wesentlich höheren Explosionsdrücken als den nach dieser Europäischen Norm gemessenen führen. Diese Europäische Norm gilt nicht für die Konstruktion und Prüfung von druckfesten Kapselungen nach den Anforderungen von EN 13463-6 (für nicht elektrische Betriebsmittel) und EN 60079-1 (für elektrische Betriebsmittel).

Détermination de la pression maximale d'explosion et de la vitesse maximale de montée en pression des gaz et des vapeurs

La présente Norme européenne spécifie une méthode d'essai conçue pour fournir des mesures de la pression d'explosion et de la pression maximale d'explosion, ainsi que des mesures de la vitesse de montée en pression et de la vitesse maximale de montée en pression d'un mélange gaz inflammable/air/gaz inerte, dans un volume clos, à température et pression ambiantes. Dans la présente Norme européenne, le terme « gaz » inclut les vapeurs mais n'inclut pas les brouillards. Les phénomènes de détonation et de décomposition explosive ne sont pas pris en compte dans la présente Norme européenne. Les pressions et les vitesses de montée en pression mesurées selon les modes opératoires spécifiés dans la présente Norme européenne ne sont pas applicables aux enveloppes antidéflagrantes, c'est-à-dire aux enveloppes destinées à résister à une explosion interne et à ne pas la transmettre à l'atmosphère explosive externe ou à tout autre volume fermé où la géométrie interne peut entraîner une accumulation de pression. Même dans une enveloppe dont la géométrie est relativement simple, la disposition des éléments internes peut conduire à des vitesses de montée en pression nettement supérieures à celles mesurées selon la présente Norme européenne. La présente Norme européenne ne s’applique pas à la conception et aux essais des enveloppes antidéflagrantes conformes à l’EN 13463-6 (pour le matériel non électrique) et à l’EN 60079-1 (pour le matériel électrique).

Ugotavljanje najvišjega tlaka eksplozije in največje hitrosti naraščanja tlaka plinov in hlapov

Ta standardna preskusna metoda je zasnovana za določevanje tlaka eksplozije in najvišjega tlaka eksplozije vnetljive mešanice plin-zrak-inertni plin pri sobni temperaturi in tlaku.
Ta standardna preskusna metoda je zasnovana za merjenja stopnje tlaka eksplozije in najvišjega tlaka eksplozije vnetljive mešanice plin-zrak-inertni plin pri sobni temperaturi in tlaku.
V tem evropskem standardu izraz »plin« vključuje hlape, vendar ne meglic. Pojava detonacije in dekompozicije nista obravnavana v tem evropskem standardu.

General Information

Status
Withdrawn
Publication Date
12-Sep-2011
Withdrawal Date
29-Mar-2022
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
28-Mar-2022
Due Date
20-Apr-2022
Completion Date
30-Mar-2022

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2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen zeitlichen Druckanstieges für Gase und DämpfeDétermination de la pression maximale d'explosion et de la vitesse maximale de montée en pression des gaz et des vapeursDetermination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours13.230Varstvo pred eksplozijoExplosion protectionICS:Ta slovenski standard je istoveten z:EN 15967:2011SIST EN 15967:2011en,fr,de01-oktober-2011SIST EN 15967:2011SLOVENSKI

STANDARDSIST EN 13673-2:2006SIST EN 13673-1:20031DGRPHãþD
SIST EN 15967:2011
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 15967

August 2011 ICS 13.230 Supersedes EN 13673-1:2003, EN 13673-2:2005English Version

Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours

Détermination de la pression maximale d'explosion et de la vitesse maximale de montée en pression des gaz et des vapeurs

Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen zeitlichen Druckanstieges für Gase und Dämpfe This European Standard was approved by CEN on 1 July 2011.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN 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 CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.

EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre:
Avenue Marnix 17,

B-1000 Brussels © 2011 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN 15967:2011: ESIST EN 15967:2011

EN 15967:2011 (E) 2 Contents Page Foreword ..............................................................................................................................................................4Introduction .........................................................................................................................................................51 Scope ......................................................................................................................................................62 Normative references ............................................................................................................................63 Terms and definitions ...........................................................................................................................64 Test method ............................................................................................................................................74.1 Principle ..................................................................................................................................................74.2 Apparatus ...............................................................................................................................................74.2.1 General ....................................................................................................................................................74.2.2 Test vessel ..............................................................................................................................................74.2.3 Equipment for preparing the test mixture ...........................................................................................84.2.4 Ignition system .......................................................................................................................................84.2.5 Pressure measuring system .................................................................................................................94.2.6 Temperature measuring device ......................................................................................................... 104.2.7 Safety aspects ..................................................................................................................................... 104.3 Preparation and preservation of test samples ................................................................................ 104.4 Procedure ............................................................................................................................................ 114.4.1 Preparation of the test mixture .......................................................................................................... 114.4.2 Determination of the explosion pressure pex, the maximum explosion pressure pmax, the rate of explosion pressure rise (dp/dt)ex and the maximum rate of explosion pressure rise (dp/dt)max ................................................................................................................................................ 124.5 Expression of results ......................................................................................................................... 144.5.1 Common aspects ................................................................................................................................ 144.5.2 Explosion pressure and maximum explosion pressure ................................................................. 154.5.3 Rate of pressure rise and maximum rate of pressure rise ............................................................. 154.6 Test report ........................................................................................................................................... 16Annex A (normative)

Verification of maximum explosion pressure values ............................................... 18Annex B (normative)

Verification of maximum rate of pressure rise ......................................................... 19Annex C (normative)

Smoothing of pressure-time curves .......................................................................... 22Annex D (informative)

Conversion of the values for the flammable substance content .......................... 25D.1 Abbreviations and symbols ............................................................................................................... 25D.2 Substance characteristics of air ....................................................................................................... 25D.3 Definitions ........................................................................................................................................... 26D.4 Preparation of the test mixture .......................................................................................................... 26Annex E (informative)

Example of an evaporator equipment for liquid flammable substances.............. 29Annex F (informative)

Example for test report form ..................................................................................... 31Annex G (informative)

Significant technical changes between this European Standard and the previous editions ................................................................................................................................ 34Annex ZA (informative)

Relationship between this European Standard and the Essential Requirements of EU Directive 94/9/EC ............................................................................................. 35Annex ZB (informative)

Relationship between this European Standard and the Essential Requirements of EU Directive 2006/42/EC ....................................................................................... 36Bibliography ..................................................................................................................................................... 37SIST EN 15967:2011

EN 15967:2011 (E) 3

Figures Figure B.1 — Plot of the rate of explosion pressure rise (dp/dt)ex as a function of the test vessel volume V for H2-air mixtures (xH2 ≅ 35 mol %) ................................................................................................................. 20 Figure B.2 — Plot of the rate of explosion pressure rise (dp/dt)ex as a function of the test vessel volume V for CH4-air mixtures (xCH4 ≅ 10 mol %) ............................................................................................................. 20 Figure B.3 — Plot of the rate of explosion pressure rise (dp/dt)ex as a function of the test vessel volume V for NH3-air mixtures (xNH3 ≅ 23 mol %) ............................................................................................................. 21 Figure C.1 — Example of a raw p(t) curve showing oscillations ........................................................................ 23 Figure C.2 — Example of a raw p(t) curve showing oscillations ........................................................................ 23 Figure C.3 — Schematic diagram showing the variation of (dp/dt)ex as a function of a smoothing parameter . 24 Figure E.1 — Evaporator equipment for producing test mixtures from liquid flammable substances ............... 29 Tables Table 1 — Rules for rounding up (dp/dt)ex and (dp/dt)max values ......................................................................... 16Table A.1 — Valuesa for verification of the apparatus ........................................................................................ 18Table B.1 — Valuesa for verification of the apparatusb ...................................................................................... 19Table D.1 — Formulas for the conversion .......................................................................................................... 28Table G.1 — The significant changes with respect to EN 13673-1:2003 and EN 13673-2:2005 ...................... 34Table ZA.1 — Correspondence between this European Standard and Directive 94/9/EC ................................ 35Table ZB.1 — Correspondence between this European Standard and Directive 2006/42/EC .......................... 36 SIST EN 15967:2011

EN 15967:2011 (E) 4 Foreword This document (EN 15967:2011) has been prepared by Technical Committee CEN/TC 305 “Potentially explosive atmospheres - Explosion prevention and protection”, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by February 2012, and conflicting national standards shall be withdrawn at the latest by February 2012. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent rights. This document supersedes EN 13673-1:2003, EN 13673-2:2005. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s). For relationship with EU Directive(s), see informative Annex ZA and B which are an integral part of this document. The significant changes between this European Standard and EN 13673-1:2003 and EN 13673-2:2005 are given in Table G.1 According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

SIST EN 15967:2011

EN 15967:2011 (E) 5 Introduction This European Standard describes test methods for the determination of:  the explosion pressure and the maximum explosion pressure; and  the rate of explosion pressure rise and the maximum rate of explosion pressure rise; of a quiescent flammable gas/air/inert mixture at ambient temperature and pressure. Maximum explosion pressure and maximum rate of explosion pressure rise are used for designing explosion protection measures, such as explosion pressure resistant or explosion pressure shock resistant apparatus, explosion venting and explosion suppression. These characteristics are particularly influenced by:  the size and shape of the vessel;  the type and energy of the ignition source;  the temperature and pressure;  the turbulence. It is therefore necessary to standardise the conditions at which the maximum explosion pressure and the maximum rate of explosion pressure rise are determined. SIST EN 15967:2011

EN 15967:2011 (E) 6 1 Scope This European Standard specifies a test method that is designed to produce measurements of explosion pressure and the maximum explosion pressure, the rate of explosion pressure rise and the maximum rate of explosion pressure rise of a quiescent flammable gas/air/inert mixture in closed volume at ambient temperature and pressure. In this European Standard, the term "gas" includes vapours but not mists. Detonation and decomposition phenomena are not considered in this European Standard. The pressures and rates of pressure rise measured by the procedures specified in this European Standard are not applicable to flameproof enclosures, that is enclosures intended to withstand an internal explosion and not to transmit it to an external explosive atmosphere, or any other closed volume where the internal geometry can result in pressure piling. Even in an enclosure of relatively simple geometry the disposition of the internal components can lead to rates of pressure rise significantly higher than those measured using this European Standard. This European Standard does not apply to the design and testing of flameproof enclosures in conformity with EN 13463-6 (for non-electrical equipment) and EN 60079-1 (for electrical equipment). 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. EN 13237, Potentially explosive atmospheres — Terms and definitions for equipment and protective systems intended for use in potentially explosive atmospheres 3 Terms and definitions For the purpose of this European Standard, the terms and definitions given in EN 13237 and the following apply. 3.1 explosion pressure

pex highest pressure occurring in a closed vessel during the explosion of a specific mixture of flammable substances with air or air and inert gases determined under specified test conditions NOTE pex is expressed as absolute pressure with gases and vapour and as overpressure with dusts. 3.2 maximum explosion pressure

pmax maximum value of explosion pressure measured in the tests for explosion pressure when the content of the flammable substances in the mixture is varied NOTE pmax is expressed as absolute pressure with gases and vapour and as overpressure with dusts. 3.3 rate of explosion pressure rise (dp/dt)ex highest value of the slope (first derivative) of the pressure-time curve (smoothed if necessary), measured in a closed vessel during the explosion of a specific mixture of flammable substances with air or air and inert substances determined under specified test conditions SIST EN 15967:2011

EN 15967:2011 (E) 7 3.4 maximum rate of explosion pressure rise (dp/dt)max maximum value of the explosion pressure rise per unit time measured in the tests when the content of the flammable substances in the mixture is varied NOTE For the purpose of this document, all pressures are expressed in bar absolute and rate of explosion pressure rises are expressed in bar/s. 4 Test method 4.1 Principle An explosive test mixture is ignited by a defined ignition source which is positioned in the centre of a test vessel. By means of a pressure measuring system the pressure-time curve that develops following the ignition of the test mixture is recorded. From the pressure- time curve the highest rate of explosion pressure rise (dp/dt)ex is calculated, and the highest pressure pex is determined. Repeat measurements are made with stepwise variations in the content of flammable gas in the mixture. a) The maximum explosion pressure pmax is determined as the maximum observed value of pex. b) The maximum rate of explosion pressure rise (dp/dt)max is determined as the maximum observed value of (dp/dt)ex 4.2 Apparatus 4.2.1 General The test apparatus consists of:  a test vessel;  equipment for preparing the test mixture;  an ignition system;  a pressure measuring system;  a temperature measuring device;  safety equipment. 4.2.2 Test vessel The test vessel shall be spherical or cylindrical. The internal volume of the test vessel shall be equal to or greater than 0,005 m3. If a cylindrical vessel is used, the length to diameter ratio shall be equal to 1. The test vessel and any equipment (valves, igniter, transducer, etc) fitted on the vessel shall be designed to withstand a maximum pressure of at least 20 bar. NOTE Guidance on the design of the test vessel can be found in EN 14460. The vessel shall be made of stainless steel or any material free of any catalytic effects and resistant to corrosion from the initial gas mixture and the products of combustion. SIST EN 15967:2011

EN 15967:2011 (E) 8 The test vessel shall be fitted with sufficient ports to allow filling, evacuating and purging. 4.2.3 Equipment for preparing the test mixture The test mixture can be prepared by a partial pressure method or mixing together flows of the component substances. This can be done in the test vessel or outside. If the test mixture is prepared by a partial pressure method, the vessel used for the preparation of the mixture shall be fitted with: a) a vacuum pump and a vacuum gauge; b) pressure gauges or manometers; c) a means of achieving a uniform test mixture (e.g. a stirrer). If the test mixture is prepared by mixing flows, the necessary components are: d) flow meters (mass or volume flow meters); e) a means of achieving a uniform test mixture (e.g. mixing chamber); f) an evaporator if liquid samples are used (see annex E for an example). The equipment for preparing the test mixture has to be designed in such a way that the flammable gas content in the test mixture is measured with a maximum uncertainty of measurement of ± 10 % relative for a flammable gas content up to 2 % mol or ± 0,2 % absolute for a flammable gas content above 2 % mol. 4.2.4 Ignition system 4.2.4.1 General The igniter shall be positioned in the centre of the test vessel. Recommended ignition systems are induction spark and fusing wire. The test report shall state which ignition source was used. For some special mixtures it may be necessary to use a different ignition system in order to achieve ignition of the mixture. If an alternative ignition source is used it shall be fully described in the test report. It is also recommended that specialist advice is sought on the interpretation of the results. 4.2.4.2 Induction spark A series of induction sparks between two electrodes is used as the ignition source. Stainless steel is a suitable material for the electrodes. The electrodes shall be positioned at the centre of the vessel. They shall be pointed rods with a maximum diameter of 4 mm. The angle of the tips shall be 60°. The distance between the tips shall be (5 ± 0,1) mm. The electrodes shall be mounted in the vessel so they are gas tight at the highest pressures generated during the test. The mounting shall be resistant to heat and the test mixture, and provide adequate electrical insulation from the test vessel body. A high voltage transformer, with a root mean square voltage of 13 kV to 16 kV (AC) and a short circuit current of 20 mA to 30 mA, shall be used for producing the ignition spark. The primary winding of the high voltage transformer shall be connected to the mains via a timer set to the required discharge time. The spark discharge time shall be adjusted to 0,2 s. If a spark discharge time of 0,2 s does not result in ignition of the test mixture, the test may be repeated with a spark discharge time of up to 0,5 s. SIST EN 15967:2011

EN 15967:2011 (E) 9 NOTE The power of the spark depends on the gas mixture and its pressure. In air at atmospheric conditions according to calorimetric and electric measurements such a source gives a spark with a power of approximately 10 W. 4.2.4.3 Fusing wire This ignition device generates an electric arc by passing an electrical current along a length of straight fusing wire connected between two metal rods. The electrical power for melting the wire and generating the arc is supplied from an isolating transformer. The ignition energy delivered by the arc depends on the duration of the arc and the power rating of the isolating transformer. The energy delivered shall be in the range 10 J to 20 J, as over this range of energies there is no significant effect on the explosion pressure. This is achieved by limiting the power rating of the isolating transformer to between 0,7 kVA and 3,5 kVA and by the use of a phase control technique. The latter is a chopping technique that allows only part of the AC waveform from the transformer secondary windings to energise the wire. Brass or stainless steel are suitable materials for the rods. The rods shall be parallel to each other with a separation distance of (5 ± 1) mm. For the fusing wire a straight length of NiCr wire (diameter 0,05 mm to 0,2 mm) shall be soldered to the tips of the metal rods. The rods shall be positioned in the test vessel so the fusing wire is at the centre of the vessel. The electrodes shall be mounted in the vessel so they are gas tight at the highest pressures generated during the test. The mounting shall be resistant to heat and the test mixture, and provide adequate electrical insulation from the test vessel body.

To reduce the time required for replacing the fusing wire after a test, the rods may be mounted in a plug that can be screwed into the test vessel wall.

The cross-section of the wires connecting the transformer to the rods shall be between 2,5 mm2 and 7 mm2. The length of the wires shall be less than 5 m. The diameter of the rods shall be between 1,5 mm and 5 mm.

If, for practical reasons, the diameter of the rods has to be less than 3 mm additional mechanical support may be necessary. 4.2.5 Pressure measuring system The pressure measuring system consists of: a) a pressure transducer;

1) The pressure transducer(s) shall be fitted in the test vessel, with the head flush with the internal wall. 2) The pressure transducer(s) shall be able to measure pressures up to 20 bar. Pressure transducers of lower range may be used if lower explosion pressures are expected. b) an amplifier; c) a data recording system.

1) The data recording system shall have a resolution of at least 12 bit and either a sampling rate of 20 kHz, or a sampling rate of 500/t ex samples per second.

2) tex is the time from ignition to the maximum explosion pressure. (see Figure C.1 and Figure C.2). d) The pressure measuring system shall have a bandwidth of at least 10 kHz To ensure reliability, two pressure measuring systems may be used.

The pressure measuring system shall have an accuracy such that the initial and explosion pressures are measured to ± 0,05 bar or better. SIST EN 15967:2011

EN 15967:2011 (E) 10 The pressure measuring system shall have a time resolution of at least 1 ms. 4.2.6 Temperature measuring device Any suitable thermocouple with appropriate recording equipment may be used to record this value. Recording the temperature is necessary, because especially pex and pmax are temperature dependent. 4.2.7 Safety aspects Ensure that all work is conducted within local and national regulations. Precautions shall be taken to safeguard the health of personnel conducting the tests against the different hazards that may occur during the test e.g.: a) to prevent a leak of the mixture or waste gases outside the vessel, the gas tightness of the vessel shall be checked;

b) to prevent rupture of the test vessel, it shall be designed to withstand a maximum pressure of at least 20 bar (see 4.2.2), as this can be assumed to be higher than the maximum explosion pressure likely to be generated during a test; c) if the test mixture is prepared in a separate vessel, this vessel and the connecting line shall be designed to withstand the maximum explosion pressure; d) to prevent injuries to the operator from flying fragments, all parts of the apparatus that may contain an explosive mixture shall be adequately shielded; e) adequate ventilation shall be provided to prevent the build up of an explosive atmosphere in the laboratory as a result 1) of purging of the apparatus; 2) exhaust from the vacuum pump;

3) or leaks from the apparatus. f) all electrical connections shall be adequately insulated to prevent electrocution or shock to personnel; g) measures shall be taken prior to preparing the mixture to ensure that the substances can be mixed without risk; h) measures shall be taken to prevent hazards arising from the handling of toxic flammables gases or combustion products; i) the handling of flammable liquids shall be carried out in such a manner that

the risk of a fire is minimised; j) the handling of gas cylinders shall be carried out in such a manner that the risk of an explosion is minimised; k) in the event of ignition system failure, the explosive mixture will still be present at the end of the test, purge and diltute to render non-flammable. 4.3 Preparation and preservation of test samples The components of the test mixture shall fulfil the following requirements: a) Air:

the air shall be free of water and oil. If synthetic air is used, it has to be stated in the

report.
SIST EN 15967:2011
EN 15967:2011 (E) 11 b) Inert:

the purity of the inert, or the mixture of inerts, shall be 99,8 % mol or better. If a mixture

of inerts is used, the composition of the mixture shall be stated in the test report.

c) Flammable gas:

the flammable gas may be derived from: 1) a single substance or a mixture of substances, 2) a process sample (of known or unknown composition). When a single substance or a mixture of substances is used, the purity of each substance shall be 99,8 % mol or better. In the case of a mixture of substances or a process sample of known composition, the precision of the composition shall be stated in the test report. In the case of a process sample of unknown composition, the sample shall be defined as well as possible (e.g. process conditions, lower explosion limit). If the flammable gas is derived from a liquid containing more than one component, the gas phase composition can differ from the composition of the liquid phase and when large quantities of the gas are drawn off, the composition of both the liquid and gas phases can change with time. For these reasons, the test sample shall be taken from the liquid phase. 4.4 Procedure 4.4.1 Preparation of the test mixture 4.4.1.1 General If liquefied gases or liquids are used, it is necessary to ensure that there is no condensation. NOTE Condensation can be prevented by checking the vapour pressure of the substances and by local heating to prevent cooling at certain parts of the apparatus (e.g. valves). The test mixture may be prepared by the method of partial pressures or by the method of mixing flows, either inside or outside the test vessel. 4.4.1.2 Preparation of the test mixture by partial pressures If the preparation of the test mixture includes evacuating the vessel, the amount of air remaining shall be taken into account when calculating the pressures of combustible substances and air required. In preparing the test mixture, precautions may be necessary to prevent condensation. The mixture components are sequentially introduced into the vessel to give the required partial pressure. The partial pressure measuring system shall have an accuracy of ± 0,005 bar or better. It is necessary to ensure that the mixture in the vessel is thoroughly mixed during the introduction of each component. If the volume of the feed lines is not negligible compared to the volume of the vessel, they also shall be evacuated or purged. NOTE For practical reasons, air is often introduced as the last component, especially if atmospheric air is used. 4.4.1.3 Preparation of the test mixture by mixing flows The test mixture is prepared by thoroughly mixing metered flows of the gaseous components. If liquid components are used, they shall be vaporised totally before mixing. NOTE It is recommended that if possible the composition of the test mixture is also measured, to check the metering devices are operating correctly and that there are no leaks in the mixing system. SIST EN 15967:2011

EN 15967:2011 (E) 12 4.4.2 Determination of the explosion pressure pex, the maximum explosion pressure pmax, the rate of explosion pressure rise (dp/dt)ex and the maximum rate of explosion pressure rise (dp/dt)max

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