SIST EN 15967:2022
(Main)Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours
Determination of maximum explosion pressure and the maximum rate of pressure rise of gases and vapours
This document specifies a test method that is designed to measure the 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 document, the term “gas” includes vapours but not mists. Detonation and decomposition phenomena are not considered in this document.
The pressures and rates of pressure rise measured by the procedures specified in this document are not applicable to flameproof enclosures, i.e. 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 document. This document does not apply to the design and testing of flameproof enclosures in conformity with EN ISO 80079-37 (for non-electrical equipment) and EN 60079-1 (for electrical equipment).
Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen zeitlichen Druckanstieges für Gase und Dämpfe
Dieses Dokument legt ein Prüfverfahren zur Bestimmung des Explosionsdruckes und des maximalen Explosions¬druckes sowie des zeitlichen Explosionsdruckanstieges und des maximalen zeitlichen Explosionsdruck¬anstieges eines ruhenden Gemischs aus brennbarem Gas, Luft und Inertgas bei Umgebungstemperatur in geschlossenen Behältern fest. In diesem Dokument schließt der Begriff „Gas“ auch Dämpfe, jedoch keine Nebel, ein. Detonations- und Zersetzungsphänomene werden in diesem Dokument nicht betrachtet.
Die nach den in diesem Dokument 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 zeitlichen Druckanstiegen als den nach diesem Dokument gemessenen führen. Dieses Dokument ist nicht anzuwenden für die Konstruktion und Prüfung von druckfesten Kapselungen nach den Anforderungen von EN ISO 80079-37 (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
Le présent document spécifie une méthode d’essai conçue pour mesurer la pression d’explosion et la pression maximale d’explosion, ainsi que la vitesse de montée en pression et 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 le présent document, 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 le présent document.
Les pressions et les vitesses de montée en pression mesurées selon les modes opératoires spécifiés dans le présent document 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 le présent document. Le présent document ne s’applique pas à la conception et aux essais des enveloppes antidéflagrantes conformes à l’EN ISO 80079-37 (pour le matériel non électrique) et à l’EN 60079-1 (pour le matériel électrique).
Ugotavljanje največjega tlaka eksplozije in največje hitrosti naraščanja tlaka plinov in hlapov
Preskusna metoda v tem evropskem standardu je zasnovana za merjenje tlaka eksplozije, največjega tlaka eksplozije, hitrosti naraščanja tlaka eksplozije in največje hitrosti naraščanja tlaka eksplozije neaktivne vnetljive mešanice plinov/zraka/inertnih plinov v zaprti prostornini pri temperaturi in zračnem tlaku okolice. Izraz »plin« v tem evropskem standardu vključuje hlape, ne pa tudi meglic. Pojavi detonacije in razkroja niso zajeti v tem evropskem standardu.
Tlaki in hitrosti naraščanja tlaka, izmerjeni s postopki iz tega evropskega standarda, se ne uporabljajo za ognjevarna ohišja, tj. ohišja, ki naj bi bila odporna na notranjo eksplozijo in naj je ne bi prenesla v zunanjo eksplozivno atmosfero ali katero koli drugo zaprto prostornino, kjer lahko notranja geometrija povzroči kopičenje tlaka. Tudi v ohišju s sorazmerno preprosto geometrijo so zaradi razporeditve notranjih sestavnih delov hitrosti naraščanja tlaka lahko znatno večje od hitrosti, izmerjenih z uporabo tega evropskega standarda. Ta evropski standard se ne uporablja za načrtovanje in preskušanje ognjevarnih ohišij v skladu s standardoma EN 13463-6 (za neelektrično opremo) in EN 60079-1 (za električno opremo).
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
01-maj-2022
Nadomešča:
SIST EN 15967:2011
Ugotavljanje največjega tlaka eksplozije in največje hitrosti naraščanja tlaka plinov
in hlapov
Determination of maximum explosion pressure and the maximum rate of pressure rise of
gases and vapours
Verfahren zur Bestimmung des maximalen Explosionsdruckes und des maximalen
zeitlichen Druckanstieges für Gase und Dämpfe
Détermination de la pression maximale d'explosion et de la vitesse maximale de montée
en pression des gaz et des vapeurs
Ta slovenski standard je istoveten z: EN 15967:2022
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN 15967
EUROPEAN STANDARD
NORME EUROPÉENNE
January 2022
EUROPÄISCHE NORM
ICS 13.230; B Supersedes EN 15967:2011
English 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 Verfahren zur Bestimmung des maximalen
de la vitesse maximale de montée en pression des gaz Explosionsdruckes und des maximalen zeitlichen
et des vapeurs Druckanstieges für Gase und Dämpfe
This European Standard was approved by CEN on 12 December 2021.
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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 15967:2022 E
worldwide for CEN national Members.
Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Test method . 7
4.1 Principle . 7
4.2 Apparatus . 7
4.2.1 General. 7
4.2.2 Test Vessel . 8
4.2.3 Equipment for preparing the test mixture . 8
4.2.4 Ignition system . 8
4.2.5 Pressure measuring system . 9
4.2.6 Initial temperature measuring device . 10
4.2.7 Safety aspects . 10
4.3 Preparation and preservation of test samples . 11
4.4 Procedure . 12
4.4.1 Preparation of the test mixture . 12
4.4.2 Determination of the explosion pressure p , the maximum explosion pressure p ,
ex max
the rate of explosion pressure rise (dp/dt) and the maximum rate of explosion
ex
pressure rise (dp/dt) . 12
max
4.5 Expression of results . 15
4.5.1 Common aspects . 15
4.5.2 Explosion pressure and maximum explosion pressure . 15
4.5.3 Rate of pressure rise and maximum rate of pressure rise . 16
4.6 Test report . 17
Annex A (normative) Verification of maximum explosion pressure values . 19
Annex B (normative) Verification of maximum rate of pressure rise . 20
Annex C (normative) Smoothing of pressure-time curves . 23
Annex D (informative) Conversion of the values for the flammable substance content. 27
D.1 Abbreviations and symbols . 27
D.2 Substance characteristics of air . 27
D.3 Definitions . 28
D.4 Preparation of the test mixture . 28
Annex E (informative) Example of an evaporator equipment for liquid flammable substances
................................................................................................................................................................... 31
Annex F (informative) Example for test report form . 33
Annex G (informative) Significant technical changes between this European Standard and
the previous editions . 36
Annex H (informative) Approximate dependence of the explosion pressure ratio on
temperature . 37
H.1 Definition of parameters . 37
H.2 Deriving an equation for approximating the temperature dependence of the
explosion pressure ratio . 37
Annex ZA (informative) Relationship between this European Standard and the essential
requirements of Directive 2014/34/EU aimed to be covered . 39
Annex ZB (informative) Relationship between this European Standard and the essential
requirements of Directive 2006/42/EC aimed to be covered . 40
Bibliography . 41
European foreword
This document (EN 15967:2022) 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 July 2022, and conflicting national standards shall be
withdrawn at the latest by July 2022.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 15967:2011.
Significant technical differences between the editions can be found in Annex G.
This document has been prepared under a Standardization Request given to CEN by the European
Commission and the European Free Trade Association, and supports essential requirements of EU
Directive(s) / Regulation(s).
For relationship with EU Directive(s) / Regulation(s), see informative Annex ZA and ZB, which are
integral parts of this document.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organisations 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, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United
Kingdom.
Introduction
This document describes test methods for the determination of:
— the 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 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 level of turbulence.
It is therefore necessary to standardize the conditions at which the maximum explosion pressure and the
maximum rate of explosion pressure rise are determined.
1 Scope
This document specifies a test method that is designed to measure the 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 document, the term “gas” includes vapours but not mists. Detonation and
decomposition phenomena are not considered in this document.
The pressures and rates of pressure rise measured by the procedures specified in this document are not
applicable to flameproof enclosures, i.e. 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 document. This document does not apply to the design and testing of flameproof enclosures in
conformity with EN ISO 80079-37 (for non-electrical equipment) and EN 60079-1 (for electrical
equipment).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 13237:2012, Potentially explosive atmospheres - Terms and definitions for equipment and protective
systems intended for use in potentially explosive atmospheres
3 Terms and definitions
For the purposes of this document, the terms and definitions given in EN 13237:2012 and the following
apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
• ISO Online browsing platform: available at https://www.iso.org/obp
• IEC Electropedia: available at https://www.electropedia.org/
3.1
explosion pressure
p
ex
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 1 to entry: is expressed as absolute pressure with gases and vapours in this standard and as overpressure
p
ex
with dusts in EN 14034.
3.2
maximum explosion pressure
p
max
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 1 to entry: p is expressed as absolute pressure with gases and vapours in this standard and as
max
overpressure with dusts in EN 14034.
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
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 1 to entry: For the purpose of this document, all pressures are expressed in kPa and rate of explosion pressure
rises are expressed in MPa/s.
3.5
scatter
modulus of the difference between the individual measured value and the mean of the three measured
values;
3.6
relative scatter
Scatter divided by the mean of the three measured values
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 is calculated, and
( )
ex
the highest pressure p is determined.
ex
Repeat measurements are made with stepwise variations in the content of flammable gas in the mixture.
a) The maximum explosion pressure p is determined as the maximum observed value of p .
max ex
b) The maximum rate of explosion pressure rise dp / dt is determined as the maximum observed
( )
max
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 m . If a cylindrical vessel is used, the length to diameter ratio shall be equal to 1 ± 0,05.
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 2 000 kPa.
NOTE Guidance on the design of the test vessel can be found in EN 14460, EN 13445-3 and EN 13480-3.
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.
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;
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 shall 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 a mole fraction of x(S) = 5 % or ± 0,5 % absolute for a flammable gas
content above a mole fraction of x(S) = 5 %.
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 ± 3) °. 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 ± 0,02) 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 ± 0,02) s.
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 energize 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 mm and
7 mm . 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 shall 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 2000 kPa. Pressure
transducers of lower range may be used if lower explosion pressures are expected.
3) The pressure transducer(s) shall have a resonance frequency of at least 20 kHz.
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
at least 20 kHz, or a sampling rate of at least 500 / t samples per second.
ex
2) t is the time from ignition to the maximum explosion pressure (see Figure C.1 and Figure C.2).
ex
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 ± 5 kPa or better.
The pressure measuring system shall have a time resolution of at least 0,1 ms.
4.2.6 Initial temperature measuring device
Any suitable thermocouple with appropriate recording equipment may be used to record this value.
Recording the initial temperature is necessary, because especially p and p are temperature
ex max
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
2 000 kPa (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) if the test mixture is prepared by mixing together flows of the component substances, measures to
prevent a destructive flashback (which may lead to a deflagration or detonation) into the piping or
mixing devices shall be implemented;
e) to prevent injuries to the operator from flying fragments, all parts of the apparatus shall be
adequately shielded in case of explosion;
f) adequate ventilation shall be provided to prevent the accumulation of flammable materials leading
to the formation of an explosive atmosphere in the laboratory as a result of:
1) purging of the apparatus;
2) exhaust from the vacuum pump; or
3) leaks from the apparatus;
g) mixtures formed during this test method will have very low ignition energies and very high explosion
pressures. Suitable precautions shall be taken to avoid ignition;
h) when analysing explosive mixtures it shall be ensured that the analysis device does not comprise an
effective ignition source where an ignition may propagate back into the apparatus;
i) all electrical connections shall be adequately insulated to prevent electrocution or shock to
personnel;
j) measures shall be taken prior to preparing the mixture to ensure that the substances can be mixed
without risk;
k) measures shall be taken to prevent hazards arising from the handling of toxic, flammable gases or
combustion products;
l) the handling of flammable liquids shall be carried out in such a manner that the risk of a fire is
minimized;
m) the handling of gas cylinders shall be carried out in such a manner that the risk of an explosion is
minimized;
n) in the event of ignition system failure, the explosive mixture will still be present at the end of the test,
purge and dilute 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 (less than 100 ppmV, respectively). If synthetic air is used,
it shall be stated in the report.
b) Inert: the purity of the inert, or the mixture of inerts, shall be x(inert) = 99,8 % 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
x(inert) = 99,8 % 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 partial 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 ± 0,2 kPa or better and a resolution
of ± 0,02 kPa 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.
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 vaporized totally before mixing.
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.
4.4.2 Determination of the explosion pressure p , the maximum explosion pressure p , the
ex max
rate of explosion pressure rise (dp/dt) and the maximum rate of explosion pressure rise
ex
(dp/dt)
max
4.4.2.1 Test procedure
The same sets of data are used for the determination of the explosion pressure and rate of explosion
pressure rise, gathered simultaneously by the same procedure.
If the test mixture is not prepared in the test vessel, fill the vessel with the test mixture either by
preliminary evacuation or by purging.
The test vessel and the feed lines shall be evacuated to a pressure of 0,5 kPa or less before filling. Purging
shall be done in such a way that the test vessel atmosphere is totally replaced. This is achieved by purging
with a volume that 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 test mixture shall be left for a period of at least two minutes to ensure it is quiescent. The test mixture
is then ignited and the pressure-time curve of the explosion recorded.
During a set of tests the temperature increase of the vessel (caused by the combustion after ignition) shall
not be allowed to exceed 15 K (see 4.5.2)
After the test residual overpressure shall be released from the test vessel. Following this, the vessel shall
be purged with air to remove the combustion products. The combustion products and purge gas shall be
discharged safely.
The humidity of the gas mixture can influence the rate of pressure rise, so it is important to ensure that
the test vessel and feed lines have been purged of all moisture before starting the next test.
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 the determination of p the number of determinations may be reduced to three, provided the
ex
relative scatter in the first three tests is not greater than 7 %.
— For the determination of (dp/dt) the number of determinations may be reduced to three, provided
ex
the relative scatter in the first three tests is not greater than 20 %.
4.4.2.2 Determination of the explosion pressure pex
The highest pressure on each of the pressure-time curves for a given composition measured by the
procedure in 4.4.2.1 is determined by one of the following methods.
a) Computational method:
A 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 10 kPa. The pressure-time-curve may be smoothed for this purpose.
b) Graphical method:
From a plot of pressure versus time, which may be the analogue output from a recording instrument,
the highest pressure shall be determined. The precision of the data used for the plot and the scale of
the graph shall be sufficient to allow the pressures to be resolved to the nearest 10 kPa.
The explosion pressure p is the highest value of these determinations.
ex
For fast reacting mixtures, the pressure time curves can show high frequency oscillations. These shall be
discounted in determining p .
ex
4.4.2.3 Determination of (dp/dt)
ex
The highest (dp/dt) on each of the pressure-time curves at the given composition is determined by the
ex
following method.
The pressure-time plot from each test is differentiated to obtain the highest value of the slope (first
derivative) for each test. In many cases it may be first necessary to smooth the raw pressure-time data,
otherwise erroneous values of the slope may be calculated. Where smoothing techniques are required
they shall conform to the requirements of Annex C.
The rate of explosion pressure rise (dp/dt) is the highest value of the slope derived from the tests.
ex
4.4.2.4 Determination of the maximum explosion pressure p and maximum rate of explosion
max
pressure rise (dp/dt)
max
The maximum explosion pressure p and maximum rate of explosion pressure rise (dp/dt) are both
max max
determined by varying stepwise the amount of flammable gas in a flammable gas/air mixture, until the
respective maxima of p and (dp/dt) are attained.
ex ex
p and (dp/dt) are both normally found for mixture compositions near the stoichiometric ratio,
max max
although they are not necessarily coincident. In order to determine the maximum explosion pressure or
maximum rate of pressure rise with sufficient accuracy and with the minimum number of measurements,
the following iterative procedure shall be used. Having determined one it may still be necessary to
perform further measurements to determine the other.
Step 1
Choose from existing knowledge, calculation or estimation, the flammable gas content at which p
max
and/or (dp/dt) is expected to occur. This chosen value of flammable gas content is taken as the
max
reference value. If the stoichiometric ratio for the reaction of the flammable gas with air can be calculated,
then 1,1 times the stoichiometric ratio may be used as the reference value. Otherwise estimate the
reference value, for example by analogy to other flammable gases of 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 stoichiometric composition.
Step 2
Follow the procedure given in 4.4.2.1, 4.4.2.2 and 4.4.2.3 for the four mixtures with a flammable gas
content of 0,8 times; 1,0 times; 1,2 times and 1,4 times the reference value. In cases where there is a high
degree of confidence that p and/or (dp/dt) occurs near the reference value, the number of
max max
mixtures may be reduced to three and the incremental value may be reduced to less than 0,2 times the
reference value.
Step 3
Calculate the mean of the three or five sets of p and/or (dp/dt) values obtained for each flammable
ex ex
gas content. Find the highest value of these means determined so far.
Step 3.1
If the highest value found in step 3 is at the highest or lowest value of flammable gas content used, then
extend the range of flammable gas content used. Choose two additional values of flammable gas content,
either at the lower or higher end of the range as appropriate, at incremental values of 0,2 times the
reference value. Otherwise proceed to step 3.2.
Step 3.2
If the highest value found in step 3 lies within the range of flammable gas content used, choose two
additional values of flammable gas content at the midpoints of the intervals to the left and right of the
point giving the highest mean.
Step 3.3
If there is more than one highest mean value, each one shall be treated separately according to step 3.1
or 3.2.
Step 4
Follow the procedure given in 4.4.2.1, 4.4.2.2 and 4.4.2.3 for the new values of flammable gas content
calculated according to steps 3.1 or 3.2.
Step 5
Repeat step 3 to step 4 until:
— for p the change in the measured values of the explosion pressures is less than the accuracy of the
max
pressure measuring system (5 kPa or better, see 4.2.5);
— or for (dp/dt) the change in mean value is less than 10 %;
max
or for either measurement
— the 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 x(S) = 2 % and ± 0,2 % absolute
for a flammable gas content above x(S) = 2 %, see 4.2.3).
Step 6
Take the highest measured value of the explosion pressure as the maximum explosion pressure p .
max
Take the highest measured value of the rate of explosion pressure rise as the maximum rate of explosion
pressure rise (dp/dt) .
max
4.5 Expression of results
4.5.1 Common aspects
In reporting results of these determinations, all the information specified in 4.6 shall be provided.
The flammable gas content shall be stated either as mole fraction, volume fraction or mass fraction. For
more details, see Annex D. For the maximum deviation of the flammable gas content, the maximum value
of ± 0,5 % absolute or the corresponding value calculated from the relative deviation of ± 10 % shall be
stated (see 4.2.3). A smaller deviation can be stated if it can be shown that the mixture was prepared to a
greater accuracy (either by the method used or from analysis of the mixture).
NOTE The specific conditions and the objective of the method described in this standard do not permit the
results to be evaluated by conventional statistical methods. They are not applicable here as the conditions regarding
the distributions of random deviations are not met and systematic deviations – caused by the influence of the
conditions of measurement – cannot be separated from random deviations.
4.5.2 Explosion pressure and maximum explosion pressure
In reporting results of these determinations, all the information specified in 4.6 shall be provided.
As the values are obtained for safety purposes, the highest values of pressure are used instead of the
mean values.
For the explosion pressure p the evaluation of the test is based on the highest pressure of 5 tests carried
ex
out with the actual 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 10 kPa. In addition, the flammable gas content in the actual test mixture shall be stated.
For the maximum explosion pressure p the evaluation of the test is based on that test mixture which
max
gives the highest explosion pressure of all. In order to take into account all uncertainties (pressure
measuring, flammable gas content, calibration), the highest value is rounded up to the nearest 10 kPa. In
addition, the flammable gas content in the test mixture which gave this highest value and the value of the
last flammable gas content increment shall be stated to indicate the accuracy of the determination.
NOTE 1 Most normal combustibles (such as hydrocarbons and hydrogen, but not halogenated compounds or
unsaturated hydrocarbons) in mixture with air, or with air and inert gas, show the following temperature and
pressure dependence of p :
max
p T , p ⋅⋅T p
T ( )
max 1 1 1
p Tp, =p⋅−1 + (1)
( )
max
T Tp⋅
1
where
T, p are initial temperature and initial pressure of the mixture, for which p is to be
max
calculated; units are K and kPa;
T , p are initial temperature and initial pressure of the mixture with same composition in
1 1
the test, by which p was determined; units are K and kPa;
max
p (T,p) is p to be calculated at T and p; unit is kPa;
max max
p (T ,p ) is p measured at T and p ; unit is kPa.
max 1 1 max 1 1
Similar dependences can be expected for p , except for near limit mixtures. If the combustibles exhibit
ex
pre-reactions at the temperature considered and for halogenated compounds and for compounds that
can decompose explosively, it is not recommended to apply the formula.
NOTE 2 Instead of specifying the explosion pressure p or the maximum explosion pressure p it is often
ex max
convenient to specify the explosion pressure ratio r and the maximum explosion pressure ratio r which are
ex max
given by p /p and p /p , respectively. Here p denotes the pressure of the mixture before ignition.
ex initial max initial initial
or r ).
In general, the explosion pressure ratio r is independent of the initial pressure (r stands for either r
ex max
The formula given in note 1 transforms to
T
rT=11+ rT − (2)
( ) ( ( ) )
T
where
r(T) is the explosion pressure ratio of the mixture at temperature T to be calculated;
T is the initial temperature of the mixture for which r is known;
T is the temperature of the mixture for which r is to be calculated;
r(T ) is the known explosion pressure ratio of the mixture at temperature T .
1 1
The verification of the apparatus and procedure shall be carried out according to Annex A.
4.5.3 Rate of pressure rise and maximum rate of pressure rise
In reporting results of these determinations, all the information specified in 4.6 shall be provided.
NOTE The values for (dp/dt) and (dp/dt) will depend on the volume and shape of the test vessel used for
ex max
the determination. For example, (dp/dt) decreases with increasing vessel volume. It is, therefore, the practice to
max
quote a rate of explosion pressure rise normalized to a vessel volume of 1 m (K ), using the following Formula (3):
G
dp
KV= (3)
G
dt
max
where
V is the vessel volume.
The above equation is based on an idealised treatment of a gas explosion, referred to as the ‘cubic law’,
which assumes K will be independent of vessel volume. However, it has been shown that this is not the
G
case [7] and that K increases with vessel volume.
G
is measured in a spherical vessel with
It is also implicit in deriving the above equation that (dp/dt)
max
central ignition. Thus for valid comparisons to be made between (dp/dt) or K values for different
max G
flammable gases, the determinations shall be carried out using the same conditions in vessels of identical
shape and volume.
For rate of explosion pressure rise (dp/dt) , the evaluation of the test is ba
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