SIST EN 13673-1:2003
(Main)Determination of the maximum explosion pressure and the maximum rate of pressure rise of gases and vapours - Part 1: Determination of the maximum explosion pressure
Determination of the maximum explosion pressure and the maximum rate of pressure rise of gases and vapours - Part 1: Determination of the maximum explosion pressure
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. In this standard, "gas" also includes vapours but not mists. Detonation phenomena are not considered in this standard.
Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen zeitlichen Druckanstieges für Gase und Dämpfe - Teil 1: Bestimmungsverfahren für den maximalen Explosionsdruck
Diese Norm legt ein Verfahren fest für das Bestimmen des Explosionsdruckes und des maximalen Explosionsdruckes ruhender Gemische aus brennbaren Gasen (Brennstoff), Luft und Inertgas bei Umgebungsbedingungen in geschlossenen Behältern ohne Einbauten. In dieser Europäischen Norm subsummiert der Ausdruck "Gas" auch Dämpfe, jedoch nicht Nebel.
Diese Europäische Norm gilt nicht für Gemische, die einen erhöhten Sauerstoffanteil aufweisen und für Gemische, die bei Umgebungsbedingungen spontan reagieren. Diese Europäische Norm gilt nicht für Bedingungen, unter denen Detonations- und Zersetzungsphänomene auftreten können.
Die nach dem hier beschriebenen Normverfahren bestimmten Drücke sind nicht anwendbar für die Auslegung druckfester Kapselung oder anderer geschlossener Behälter, deren innere Geometrie zu überdurchschnittlich hohen Explosionsdrücken aufgrund von Vorkompression führen kann. Druckfeste Kapselung ist eine Umschließung, die im Innern stattfindenden Explosionen standhält und deren Übertragung in äußere explosionsfähige Atmosphären verhindert. Selbst in Umschließungen relativ einfacher Geometrie können Einbauten zu deutlich höheren Explosionsdrücken als nach dieser Europäischen Norm bestimmt führen. Druckfeste Kapselung sollte für elektrische Betriebsmittel nach den Anforderungen in EN 50018 und für nicht elektrische Betriebsmittel nach den Anforderungen in prEN 13463-3 ausgelegt und geprüft werden.
Détermination de la pression maximale d'explosion et de la vitesse maximale de montée en pression des gaz et vapeurs - Partie 1: Détermination de la pression maximale d'explosion
La présente méthode d'essai normalisée est conçue pour déterminer la pression d'explosion et la pression maximale d'explosion d'un mélange gaz combustible/air/gaz inerte, contenu au repos dans un récipient fermé vide d'obstacles, a température et pression ambiantes. Dans la présente Norme européenne, le terme « gaz » inclut les vapeurs mais n'inclut pas les brouillards.
La présente Norme européenne ne s'applique pas aux mélanges contenant de l'air enrichi en oxygene ; ou des mélanges réagissant spontanément a la température ambiante et a la pression. Les phénomenes de détonation et de décomposition explosive ne sont pas pris en compte dans la présente Norme européenne.
Les pressions mesurées selon les modes opératoires définis dans la présente Norme européenne ne s'appliquent pas aux enveloppes antidéflagrantes, c'est-a-dire aux enveloppes destinées a résister a une explosion interne et a ne pas la transmettre a une atmosphere explosive externe, ou a tout autre volume fermé ou la géométrie interne peut induire un accroissement de la pression. Meme dans une enveloppe de géométrie relativement simple, la disposition des équipements internes peut conduire a des pressions d'explosion significativement supérieures a celles mesurées selon la présente Norme européenne. Les enveloppes antidéflagrantes doivent etre construites et soumises a essai conformément aux exigences des normes EN 50018 pour les appareils électriques et prEN 13463-3 pour les appareils non-électriques.
Ugotavljanje najvišjega tlaka eksplozije in največje hitrosti naraščanja tlaka plinov in hlapov - 1. del: Ugotavljanje najvišjega tlaka eksplozije
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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 Dämpfe - Teil 1: Bestimmungsverfahren für den maximalen ExplosionsdruckDétermination de la pression maximale d'explosion et de la vitesse maximale de montée en pression des gaz et vapeurs - Partie 1: Détermination de la pression maximale d'explosionDetermination of the maximum explosion pressure and the maximum rate of pressure rise of gases and vapours - Part 1: Determination of the maximum explosion pressure13.230Varstvo pred eksplozijoExplosion protectionICS:Ta slovenski standard je istoveten z:EN 13673-1:2003SIST EN 13673-1:2003en,fr,de01-junij-2003SIST EN 13673-1:2003SLOVENSKI
STANDARD
SIST EN 13673-1:2003
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 13673-1April 2003ICS 13.230; 75.160.30English versionDetermination of the maximum explosion pressure and themaximum rate of pressure rise of gases and vapours - Part 1:Determination of the maximum explosion pressureDétermination de la pression maximale d'explosion et de lavitesse maximale de montée en pression des gaz etvapeurs - Partie 1: Détermination de la pression maximaled'explosionVerfahren zur Bestimmung des maximalenExplosionsdruckes und des maximalen zeitlichenDruckanstieges für Gase und Dämpfe - Teil 1:Bestimmungsverfahren für den maximalen ExplosionsdruckThis European Standard was approved by CEN on 2 January 2003.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the 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 translationunder the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and UnitedKingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2003 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 13673-1:2003 ESIST EN 13673-1:2003
EN 13673-1:2003 (E)2ContentspageForeword.3Introduction.41Scope.52Terms and definitions.53Test method.53.1Principle.53.2Apparatus.53.2.1Test vessel.63.2.2Equipment for preparing the test mixture.63.2.3Ignition system.63.2.4Pressure measuring system.73.2.5Temperature measuring device.83.2.6Safety aspects.83.3Preparation and preservation of test samples.83.4Procedure.93.4.1Preparation of the test mixture.93.4.2Determination of the explosion pressure Pex and the maximum explosion pressure Pmax.93.5Expression of results.113.6Test report.12Annex A (normative)
Verification.14Annex B (informative)
Conversion of the values for the flammable substance content.15B.1Abbreviations and symbols.15B.2Substances characteristics of air.16B.3Definitions.16B.4Preparation of the test mixture.16B.5Conversion.17Annex C (informative)
Example of an evaporator equipment for liquid flammable substances.19Annex D (informative)
Example for test report form.21Annex ZA (informative)
Clauses of this European Standard addressing essential requirements or otherprovisions of EU Directives.23SIST EN 13673-1:2003
EN 13673-1:2003 (E)3ForewordThis document (EN 13673-1:2003) has been prepared by Technical Committee CEN /TC 305, "Potentiallyexplosive 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 orby endorsement, at the latest by October 2003, and conflicting national standards shall be withdrawn at the latestby October 2003.This document has been prepared under a mandate given to CEN by the European Commission and the EuropeanFree Trade Association, and supports essential requirements of EU Directive(s).For relationship with EU Directive(s), see informative annex ZA which is an integral part of this document.Annexes B, C and D are informative.Annex A is normative.According to the CEN/CENELEC Internal Regulations, the national standards organizations of the followingcountries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal,Slovakia, Spain, Sweden, Switzerland and the United Kingdom.SIST EN 13673-1:2003
EN 13673-1:2003 (E)4IntroductionThis European Standard describes a test method for the determination of the explosion pressure and the maximumexplosion pressure of a flammable gas/air/inert mixture at ambient temperature and pressure.Explosion pressures and maximum explosion pressures are used in the design of explosion protection techniques,such as explosion resistant and explosion shock resistant construction. These are particularly influenced by :¾ size and shape of the vessel;¾ type and energy of the ignition source;¾ temperature and pressure.So it is important that they are measured at standardised conditions.SIST EN 13673-1:2003
EN 13673-1:2003 (E)51 ScopeThe standard test method is designed to produce measurement of the explosion pressure and the maximumexplosion pressure of a quiescent flammable gas/air/ inert mixture in an empty closed volume at ambienttemperature and pressure. In this European Standard the term “gas” includes vapours, but not mists. This European Standard does not consider mixtures that contain an increased content of oxygen; or mixtures thatwill react spontaneously at ambient temperature and pressure. Detonation and decomposition phenomena are notconsidered in this European Standard.The pressures measured by the procedures specified in this European Standard are not applicable to flameproofenclosures, that is enclosures intended to withstand an internal explosion and not to transmit it to an externalexplosive atmosphere, or any other closed volume where the internal geometry can result in pressure piling.
Evenin an enclosure of relatively simple geometry the disposition of the internal components can lead to explosionpressures significantly higher than those measured using this European Standard.
Flameproof enclosures shouldbe constructed and tested in accordance with the requirements contained in EN 50018 for electrical equipment andprEN 13463-3 for non-electrical equipment.2 Terms and definitionsFor the purposes of this European Standard, the following terms and definitions apply.2.1explosion pressure, Pexhighest pressure occurring in a closed vessel during the explosion of a specific mixture of flammable gases with airor air and inert gases determined under specified test conditions2.2maximum explosion pressure, Pmaxmaximum value measured in the tests for explosion pressure when the content of the flammable gas in the mixtureis variedNOTEFor the purpose of this European Standard, all pressures are expressed in bar absolute.3 Test method3.1 PrincipleAn explosive test mixture is ignited by a defined ignition source which is positioned in the centre of a test vessel. Bymeans of a pressure measuring system, the highest pressure Pex developed following the ignition of the testmixture is measured.The maximum explosion pressure Pmax is determined during measurements of the explosion pressure Pex byvarying stepwise the content of flammable gas in the mixture, until the maximum value of Pex is found.3.2 Apparatus3.2.1 GeneralThe test apparatus consists of :¾ a test vessel;¾ equipment for preparing the test mixture;¾ an ignition system;¾ a pressure measuring system;SIST EN 13673-1:2003
EN 13673-1:2003 (E)6¾ a temperature measuring device;¾ safety equipment.3.2.2 Test vesselThe test vessel shall be spherical or cylindrical. The internal volume of the test vessel shall be equal to or greaterthan 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,.) fitted on the vessel shall be designed towithstand a maximum pressure of at least 20 bar.The vessel shall be made of stainless steel or any material free of any catalytic effects and resistant to corrosionfrom the initial gas mixture and the products of combustion.The test vessel shall be fitted with sufficient ports to allow filling, evacuating and purging.3.2.3 Equipment for preparing the test mixtureThe test mixture can be prepared by a partial pressure method or mixing together flows of the componentsubstances. 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 shallbe fitted with :¾ a vacuum pump and a vacuum gauge;¾ pressure gauges or manometers;¾ 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 :¾ flow meters (mass or volume flow meters);¾ a means of achieving a uniform test mixture (e.g. mixing chamber);¾ an evaporator if liquid samples are used (see annex C for an example).The equipment for preparing the test mixture has to be designed in such a way that the flammable gas content inthe test mixture is measured with a maximum uncertainty of measurement of ± 10 % relative for a flammable gascontent up to 2 % mol or ± 0,2 % absolute for a flammable gas content above 2 % mol.3.2.4 Ignition system3.2.4.1 GeneralThe igniter shall be positioned in the centre of the test vessel. Recommended ignition systems are the inductionspark and the 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 themixture. If an alternative ignition source is used it shall be fully described in the test report. It is also recommendedthat specialist advice is sought on the interpretation of the results.3.2.4.2 Induction sparkA series of induction sparks between two electrodes is used as the ignition source.SIST EN 13673-1:2003
EN 13673-1:2003 (E)7Stainless steel is a suitable material for the electrodes. The electrodes shall be positioned at the centre of thevessel. They shall be pointed rods with a maximum diameter of 4 mm. The angle of the tips shall be 60°. Thedistance between the tips shall be (5 ± 0,1) mm. The electrodes shall be mounted in the vessel so they are gastight at the highest pressures generated during the test. The mounting shall be resistant to heat and the testmixture, and provide adequate electrical resistance from the test vessel body.A high voltage transformer, with a root mean square of 13 kV to 16 kV and a short circuit current of 20 mA to 30mA, shall be used for producing the ignition spark. The primary winding of the high voltage transformer shall beconnected 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 ofthe test mixture, the test may be repeated with a spark discharge time of up to 0,5 s.NOTE The power of the spark depends on the gas mixture and its pressure. In air at atmospheric conditions according tocalorimetric and electric measurements such a source gives a spark with a power of approximately 10 W.3.2.4.3 Fusing wireNOTE 1This ignition device generates an electric arc by passing an electrical current along a length of straight fusing wireconnected between two metal rods.NOTE 2The electrical power for melting the wire and generating the arc is supplied from an isolating transformer. The ignitionenergy delivered by the arc depends on the duration of the arc and the power rating of the isolating transformer. The energydelivered shall be in the range 10 J to 20 J, as over this range of energies there is no significant effect on the explosionpressure. This is achieved by limiting the power rating of the isolating transformer to between 0,7 kVA and 3,5 kVA and by theuse of a phase control technique. The latter is a chopping technique that allows only part of the AC waveform from thetransformer 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 aseparation 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 atthe centre of the vessel. The electrodes shall be mounted in the vessel so they are gas tight at the highestpressures generated during the test. The mounting shall be resistant to heat and the test mixture, and provideadequate electrical resistance 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 bescrewed 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. Thelength 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 benecessary.3.2.5 Pressure measuring systemThe pressure measuring system consists of a pressure transducer; an amplifier and recording equipment. Toensure reliability, two pressure measuring systems may be used.The pressure transducer(s) shall be fitted in the test vessel, with the head flush with the internal wall.The pressure transducer(s) shall have a resonance frequency greater than 10 kHz.The pressure transducer(s) shall be able to measure pressures up to 20 bar. Pressure transducers of lower rangemay be used if lower explosion pressures are expected.The pressure measuring system shall have an accuracy such that the initial and explosion pressures are measuredto ± 0,05 bar or better.The pressure measuring system shall have a time resolution of at least 1 ms.SIST EN 13673-1:2003
EN 13673-1:2003 (E)83.2.6 Temperature measuring deviceAny suitable thermocouple with appropriate recording equipment may be used.3.2.7 Safety aspectsPrecautions shall be taken to safeguard the health of personnel conducting the tests against the different hazardsthat may occur during the test e.g.:¾ to prevent a leak of the mixture or waste gases outside the vessel, the gas tighteners of the vessel shall bechecked;¾ to prevent rupture of the test vessel, it shall be designed to withstand a maximum pressure of at least 20 bar(see 3.2.2), as this can be assumed to be higher than the maximum explosion pressure likely to be generatedduring a test;¾ if the test mixture is prepared in a separate vessel, this vessel and the connecting line shall be designed towithstand the maximum explosion pressure;¾ to prevent injuries to the operator from flying fragments, all parts of the apparatus that may contain anexplosive mixture shall be adequately shielded;¾ adequate ventilation shall be provided to prevent the build up of an explosive atmosphere in the laboratory asa result¾ of purging of the apparatus;¾ exhaust from the vacuum pump;¾ or leaks from the apparatus.¾ all electrical connections shall be adequately shielded to prevent electrocution or shock to personnel;¾ measures shall be taken prior to preparing the mixture to ensure that the substances can be mixed without risk¾ measures shall be taken to prevent hazards arising from the handling of toxic flammables gases or combustionproducts;¾ the handling of flammable liquids shall be carried out in such a manner that
the risk of a fire is minimised;¾ the handling of gas cylinders shall be carried out in such a manner that the risk of an explosion is minimised.3.3 Preparation and preservation of test samplesThe components of the test mixture shall fulfil the following requirements :Air: the air shall be free of water and oil. If synthetic air is used, it shall to be stated in the report.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, thecomposition of the mixture shall be stated in the test report.Flammable gas: the flammable gas may be derived from:a) a single substance or a mixture of substances,b) 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 orbetter. In the case of a mixture of substances or a process sample of known composition, the precision of theSIST EN 13673-1:2003
EN 13673-1:2003 (E)9composition shall be stated in the test report. In the case of a process sample of unknown composition, the sampleshall 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 candiffer from the composition of the liquid phase and when large quantities of the gas are drawn off, the compositionof both the liquid and gas phases can change with time. For these reasons, the test sample shall be taken from theliquid phase.3.4 Procedure3.4.1 Preparation of the test mixture3.4.1.1 GeneralIf liquefied gases or liquids are used, it is necessary to ensure that there is no condensation.NOTECondensation can be prevented by checking the vapour pressure of the substances and by local heating to preventcooling 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 insideor outside the test vessel.3.4.1.2 Preparation of the text mixture by partial pressuresIf the preparation of the test mixture includes evacuating the vessel, the amount of air remaining shall be taken intoaccount 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 sequently introduced into the vessel to give the required partial pressure. The partialpressure measuring system shall have an accuracy of ± 0,005 bar or better. It is necessary to ensure that themixture in the vessel is thoroughly mixed during the introduction of each component. If the volume of the feed linesis not negligible compared to the volume of the vessel, they also shall be evacuated or purged.NOTEFor practical reasons, air is often introduced as the last component, especially if atmospheric air isused.3.4.1.3 Preparation of the test mixture by mixing flowsThe 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.NOTEIt is recommended that if possible the composition of the test mixture is also measured, to check the meteringdevices and that there are no leaks in the mixing system.3.4.2 Determination of the explosion pressure Pex and the maximum explosion pressure Pmax3.4.2.1 Test procedureIf the test mixture is not prepared in the test vessel, fill the vessel with the test mixture either by preliminaryevacuation or by purging.The test vessel and the feed lines shall be evacuated to a pressure of 5 mbar or less before filling. Purging shall bedone in such a way that the test vessel atmosphere is totally replaced. This is achieved by purging with a volumethat is at least ten times the vessel volume.Once the test mixture has been introduced into the test vessel, the inlet and outlet valves shall be closed. The testmixture shall be left for a period of at least two minutes to ensure it is quiescent. The test mixture is then ignitedand the pressure-time curve of the explosion recorded.SIST EN 13673-1:2003
EN 13673-1:2003 (E)10After the test, the vessel shall be purged with air to remove the combustion products. The combustion products andpurging shall be discharged safely. Before purging begins, any residual overpressure shall be released from thetest vessel.If soot is formed during the test, the test vessel and the igniter shall be cleaned.The whole test procedure shall be carried out five times for each composition of the test mixture. For determinationof Pmax the number of determinations may be reduced to three, provided the scatter in the three tests is not greaterthan 0,5 bar.3.4.2.2 Determination of the explosion pressure PexThe highest pressure on each of the five pressure-time curves measured by the procedure in 3.4.2.1 is determinedby one of the following methods.Graphical methodFrom a plot of pressure versus time, which may be the analogue output from a recording instrument, thehighest pressure shall be determined. The precision of the data used for the plot and the scale of the graphshall be sufficient to allow the pressures to be resolved to the nearest 0,1 bar.Computational methodA computer programme may be used to process the pressure-time data to determine the highest pressure.The precision of data used shall be sufficient to allow the pressures to be resolved to the nearest 0,1 bar.The explosion pressure Pex is the highest value of these five determinations.For fast reacting mixtures, the pressure time curves can show high frequency oscillations. These shall bediscounted in determining Pex.3.4.2.3 Determination of the maximum explosion pressure PmaxThe maximum explosion pressure Pmax is determined by varying stepwise the amount of flammable gas in aflammable gas/air mixture, until the maximum Pex is attained.Pmax is normally found for mixture compositions near the stoichiometric ratio. In order to determine the maximumexplosion pressure with sufficient accuracy and with the minimum number of measurements, the following iterativeprocedure shall be used.Step 1Choose from existing knowledge, calculation or estimation, the flammable gas content at which Pmax is expected tooccur. This chosen value of flammable gas content is taken as the reference value. If the stoichiometric ratio for thereaction of the flammable gas with oxygen can be calculated, then 1,1 times the stoichiometric ratio may be usedas the reference value. Otherwise estimate the reference value , for example by analogy to other flammable gasesof similar composition or in the same homologous series. In the case of process samples of unknown composition,it is recommended that twice the value of the lower explosion limit is used as an estimate of the stoichiometriccomposition.Step 2Follow the procedure given in 3.4.2.1 and 3.4.2.2 for the four mixtures with a flammable gas content of 0,8; 1,0; 1,2and 1,4 times the reference value. In cases where there is a high degree of confidence that Pmax occurs near thereference value, the number of mixtures may be reduced to three and the incremental value may be reduced toless than 0,2 times the reference value.Step 3.1Calculate the mean of the three or five pressure values obtained for each flammable gas content. Find the highestvalue of these means determined so far.SIST EN 13673-1:2003
EN 13673-1:2003 (E)11Step 3.2.1If the highest value found in step 3.1 is at the highest or lowest value of flammable gas content used, then extendthe range of flammable gas content used. Choose two additional values of flammable gas content, either at thelower or higher end of the range as appropriate, at incremental values of 0,2 times the reference value. Otherwiseproceed to step 3.2.2.Step 3.2.2If the highest value found in step 3.1 lies within the range of flammable gas content used, choose two additionalvalues of flammable gas content at the midpoints of the intervals to the left and right of the point giving the highestmean.Step 3.2.3If there are more than one highest mean value, each one shall be treated separately according to step 3.2.1 or3.2.2.Step 3.3Follow the procedure given in 3.4.2.1 and 3.4.2.2 for the new values of flammable gas content calculated accordingto steps 3.2.1 or 3.2.2.Step 4Repeat steps 3.1 to 3.3 until :either the change in the measured values of the explosion pressures is less than the accuracy of the pressuremeasuring system (0,05 bar or better, see 3.2.5);orthe flammable gas content increment is less than the accuracy of the equipment used for preparing the test mixture(± 10 % relative for a flammable gas content up to 2 % mol and ± 0,2 % absolute for a flammable gas contentabove 2 % mol, see 3.2.3).Step 5Take the highest measured value of the explosion pressure as the maximum explosion pressure.3.5 Expression of resultsIn reporting results of these determinations, all the information specified in 3.6 shall be provided.For explosion pressure Pex the evaluation of the test is based on the highest pressure of 5 tests carried out with theactual test mixture. In order to take into account all uncertainties (pressure measuring, flammable gas content,calibration, procedure with limited number of tests) this value is rounded up to the nearest 0,1 bar. In addition, theflammable gas content in the actual test mixture shall be stated.For maximum explosion pressure Pmax the evaluation of the test is based on that test mixture which gives thehighest explosion pressure of all. In order to take into account all uncertainties (pressure measuring, flammable gascontent, calibration), the highest value is rounded up to the nearest 0,1 bar. In addition, the flammable gas contentin the test mixture which gave this highest value and the value of the last flammable gas content increment shall bestated to indicate the accuracy of the determination.NOTEMany substances show for temperatures up to 200°C and pressures up to 2 bar the following temperature andpressure dependence for Pmax :SIST EN 13673-1:2003
EN 13673-1:2003 (E)12T: temperature of the mixture before ignition in KT1:reference temperaturein Kp:pressure of the mixture before ignition in barp1:reference pressurein barPmax
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