EN 1839:2012

SLOVENSKI STANDARD
01-januar-2013
1DGRPHãþD
SIST EN 1839:2003
Ugotavljanje mej eksplozivnosti plinov in hlapov
Determination of explosion limits of gases and vapours
Bestimmung der Explosionsgrenzen von Gasen und Dämpfen
Détermination des limites d'exposivité des gaz et vapeurs
Ta slovenski standard je istoveten z: EN 1839:2012
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 1839
NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2012
ICS 13.230 Supersedes EN 1839:2003
English Version
Determination of explosion limits of gases and vapours
Détermination des limites d'exposivité des gaz et vapeurs Bestimmung der Explosionsgrenzen von Gasen und
Dämpfen
This European Standard was approved by CEN on 27 July 2012.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United
Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2012 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 1839:2012: E
worldwide for CEN national Members.

Contents Page
Foreword . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Test Methods . 7
4.1 Method T (“tube” method) . 7
4.1.1 Principle . 7
4.1.2 Reagents and Materials . 7
4.1.3 Apparatus . 8
4.1.4 Preparation of the test mixture . 10
4.1.5 Procedure . 10
4.2 Method B ("bomb" method) . 11
4.2.1 Principle . 11
4.2.2 Reagents and materials . 11
4.2.3 Apparatus . 11
4.2.4 Preparation of the test mixture . 13
4.2.5 Procedure . 13
4.3 Recording of results . 15
4.4 Test report . 15
Annex A (normative) Method for determination of the explosion limits of substances that are difficult
to ignite . 17
A.1 Background . 17
A.2 Explanation . 17
A.3 Apparatus . 17
A.4 Safety equipment . 18
A.5 Preparation of the test mixture . 18
A.6 Procedure . 18
Annex B (informative) Examples to describe flame detachment . 20
Annex C (informative) Example of recommended evaporator equipment . 21
Annex D (normative) Safety measures . 23
D.1 General . 23
D.2 General safety measures . 23
D.3 Additional safety measures concerning the tube method . 23
)
Annex E (informative) Example of a form expressing the results Test report . 24
Annex F (normative) Verification . 25
Annex G (informative) Conversion of the values for the explosion limits . 27
G.1 Abbreviations and symbols . 27
G.2 Substance characteristics of air . 27
G.3 Definitions . 28
G.4 Mixture preparation . 28
G.5 Conversion . 29
Annex H (informative) Significant Changes between this European Standard and EN 1839:2003 . 31
Annex ZA (informative) Relationship between this European Standard and the Essential Requirements
of EU Directive 94/9/EC . 32
Bibliography . 33

Foreword
This document (EN 1839:2012) 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 March 2013, and conflicting national standards shall be withdrawn at the latest by
March 2013.
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 1839:2003.
The significant changes between this European Standard and EN 1839:2003 are given in Table H.1.
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 94/9/EC.
For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this document.
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, Former Yugoslav Republic of Macedonia, France, Germany, Greece,
Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,
Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.
Introduction
The hazard of an explosion can be avoided by preventing the formation of explosive mixtures of gases and/or
vapours. To do so, the explosion limits (also known as “flammability limits") of the flammable substance need to be
known. These limits depend mainly on:
 the properties of the flammable substance;
 temperature and pressure;
 size and shape of the test vessel;
 ignition source (type, energy);
 the criterion for self-propagating combustion.
To obtain reliable and comparable results it is necessary to standardise the conditions for determining the
explosion limits (i.e. apparatus and procedure). However, it is not possible to provide one single method that is
suitable for all types of substances. For practical reasons, it is preferable to use apparatus that can also be used for
the determination of other explosion characteristics. This European Standard, therefore, details two methods,
namely, the tube method (method T) and the bomb method (method B). In general, the tube method gives a wider
explosion range. Differences in the explosion limits determined by the two methods can vary by up to 10 % relative.
For substances which are difficult to ignite with large quenching distances, only a modified tube method is suitable.
This is described in Annex A.
1 Scope
This European Standard specifies two test methods (method T and method B) to determine the explosion limits of
gases, vapours and their mixtures, mixed with air. An air/inert gas mixture (volume fraction of the oxygen < 21 %)
can be used as the oxidizer instead of air. In this European Standard, the term “air” includes such air/inert mixtures.
This European Standard applies to gases, vapours and their mixtures at atmospheric pressure for temperatures up
to 200 °C.
2 Normative references
Not applicable.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
explosion range
range of the concentration of a flammable substance or mixture of substances in air, within which an explosion can
occur, respectively range of the concentration of a flammable substance or mixture of substances in mixture with
air/inert gas, within which an explosion can occur, determined under specified test conditions
[SOURCE: EN 13237:2012, 3.22]
3.2
lower explosion limit
LEL
lowest concentration of the explosion range at which an explosion can occur
Note 1 to entry: Those concentrations are given at which an explosion just fails during the tests.
[SOURCE: EN 13237:2012, 3.19.1]
3.3
upper explosion limit
UEL
highest concentration of the explosion range at which an explosion can occur
Note 1 to entry: Those concentrations are given at which an explosion just fails during the tests.
[SOURCE: EN 13237:2012, 3.19.2]
3.4
explosion criterion — flame detachment
in method T, the criterion for an explosion (self-propagating combustion) is the upward movement of the flame from
the spark gap for at least 100 mm or the formation of a halo which either reaches the top of the tube or reaches a
minimum height of 240 mm
Note 1 to entry: Throughout the duration of the ignition, spark test mixtures, whose test substance content lies just outside
the explosion range, may exhibit a luminous phenomenon (referred to as a “halo”) above the spark gap which does not detach
from the latter (see Annex B). For some test substances (e.g. halogenated hydrocarbons), this luminous phenomenon can
occupy a large portion of the test vessel. The formation of a halo alone is not considered to count as an ignition of the test
mixture unless it reaches the top of the tube or a minimum height of 240 mm.
3.5
explosion criterion — pressure rise
in method B, the criterion for an explosion (self-propagating combustion) is the generation of explosion
overpressure which is equal to or greater than the overpressure created by the ignition source alone in air plus
(5 ± 0,1) % of the initial pressure
3.6
vapour
gaseous phase emanating or being emanated from a liquid
Note 1 to entry: If not otherwise mentioned, the term “gas” in this standard also includes such vapours but not mists.
3.7
oxidizer
air or an air/inert gas mixture (volume fraction of the oxygen < 21 %)
3.8
sample
substance or mixture of substances for which explosion limits are to be determined
3.9
test substance
sample in the gaseous state; in the case of liquid samples, after complete evaporation
3.10
test mixture
mixture of test substance and air
4 Test Methods
4.1 Method T (“tube” method)
4.1.1 Principle
The test mixture flows through the cylindrical test vessel from the bottom upwards to the top until the contents
previously in the test vessel have been completely replaced. Then, under quiescent conditions, an ignition is
initiated using a series of induction sparks. It is observed whether or not flame detachment occurs. The test
substance content of the test mixture is varied stepwise until the LEL or the UEL (explosion criterion — flame
detachment) have been determined or until it is established that there is no explosion range.
4.1.2 Reagents and Materials
4.1.2.1 Air, which shall be free of water (≤0,1 mol% water vapour absolute) and oil (≤0,1 g/m oil).
If synthetic air is used, it has to be stated in the report.
4.1.2.2 Inert gases, 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.
4.1.2.3 Flammable substances, which may be either a single substance or a defined mixture of substances or a
process sample (of known or unknown composition).
When a single substance or a defined 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 process conditions.
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. When large volumes of the gas are removed, 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.
4.1.2.4 Heat-resistant, chemically inert material for gaskets and adhesive mountings.
Sample containers shall be kept closed before and after sampling to avoid changes in the sample composition
within the container (e.g. loss of volatile components from mixtures). If a sample container contains a mixture with
both gaseous and liquid phases present, the mixture composition of the two phases will be different. Under such
conditions, it is recommended that the test substance sample be removed from the liquid phase. If the sample is
taken from the gaseous phase, account must be taken of the difference in composition.
4.1.3 Apparatus
4.1.3.1 Test vessel.
The test vessel is an upright cylindrical vessel made of glass or other transparent material (e.g. polycarbonate) with
an inner diameter of (80 ± 2) mm and a minimum length of 300 mm.
The vessel is equipped with an inlet pipe with a three-way valve for the test mixture, located at the bottom, and an
outlet pipe and pressure vent in the upper part.
The bottom and top may be made of other material. However, the material must be free of any catalytic effect and
resistant to corrosion from the test mixture or the reaction products.
4.1.3.2 Ignition source.
A series of induction sparks between two electrodes is used as the ignition source.
The electrodes shall end (60 ± 1) mm above the bottom of the test vessel.
Stainless steel is a suitable material for the electrodes. The electrodes shall be pointed rods with a diameter of
maximum 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 that 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 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
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 the ignition
of the test mixture, the test may be repeated with a spark discharge time of up to 0,5 s.
The power of the induction sparks is dependent 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.
4.1.3.3 Equipment for preparing the test mixture.
The test mixture is prepared by mixing flows of gaseous components. This requires the following equipment:
 metering device for air, gaseous samples or additional inert gases (e.g. mass flow controller, volume flow
controller, metering pump for gases);
 metering device for liquid samples (e.g. volumetric metering pumps);
 evaporator equipment in the case of a liquid sample (for example see Annex C);
 mixing vessel for homogenizing the test mixture.
The metering devices and the equipment for preparing the test mixture have to be designed in such a way that the
uncertainty of measurement of the test substance content in the test mixture is not higher than the data given in
Table 1.
Table 1 — Maximum permissible uncertainty of measurement for the amount of test substance in the test
mixture
molar amount of test substance maximum uncertainty of measurement
% %
relative absolute
± 10
≤ 2
> 2 ± 0,2
4.1.3.4 Temperature regulating system.
For measurements at temperatures above ambient temperature, the apparatus requires a temperature regulating
system. When this is used, it has to be ensured that the temperature difference inside the test vessel is not more
than 10 K. This has to be checked when initially setting up the apparatus, whenever parts are renewed and at
every verification.
Key
1 test vessel    7 timer
2 electrodes    8 facility for keeping the temperature
3 three-way valve   9 flammable substance
4 mixing vessel   10 air
5 metering devices   11 power supply
6 high-voltage transformer
Figure 1 — Scheme of the ‘tube’ apparatus for determining the explosion limits
4.1.3.5 Safety equipment.
The safety measures specified in Annex D shall be followed.
4.1.4 Preparation of the test mixture
When evaporating liquid samples, it is important to remember that the mixture composition of the gaseous phase in
equilibrium with a liquid phase (”vapour”) generally differs from the mixture composition of the liquid phase itself.
Furthermore, the mixture compositions of the liquid and the vapour phases may change when removing material
from the vapour phase. Allowance for this is necessary when determining explosion limits for flammable liquids,
when handling liquid samples and when preparing test mixtures by evaporating liquid samples. To avoid error, the
method of dynamic total evaporation is used. An example of a suitable evaporator set up is described in Annex C.
When liquids are metered, it has to be ensured that bubbles are not formed in any component carrying the liquid
(e.g. pipes). To achieve complete homogenization, the test mixture flows through a mixing vessel, preferably made
of glass. For a mixing vessel with no built-in elements, a volume of at least 600 ml is recommended. It is expedient
to introduce the test mixture tangentially. The mixing vessel is not necessary if homogenization is effectively
achieved by the metering device. The temperature of the mixing vessel and of all parts carrying the test mixture is
kept constant to prevent the test substance from condensing. It is recommended that the components carrying the
test mixture are heated along with the test vessel.
4.1.5 Procedure
If the explosion limits are to be determined at elevated temperature, preheat the test vessel and all parts carrying
the test mixture to the required temperature. For liquid samples, the temperature of the test mixture shall be at least
25 K higher than the condensation temperature. Prior to each ignition attempt, it has to be ensured that the
temperature in the test vessel differs by no more than 5 K from the required value.
The determination of the explosion limits consists of a series of ignition tests which are carried out with test
mixtures whose test substance content is varied.
For safety reasons, the initial ignition tests are carried out using a test mixture with test substance content which, if
possible, lies outside the expected explosion range.
For organic substances which consist exclusively of carbon, hydrogen and oxygen (with the exception of
peroxides), the LEL can be roughly estimated. At 20 °C, the LEL, in many cases, is approximately half the test
substance content of the stoichiometric composition. The temperature dependence of the LEL has to be taken into
account. Up to 200 °C, the LEL decreases more or less linearly between 30 % and 50 % of the value estimated for
20 °C.
There is currently no method which readily estimates the UEL.
Prior to each ignition attempt, the test vessel is purged with the test mixture. The purging volume has to be at least
ten times the volume of the test vessel. When purging is complete, the inlet to the test vessel is sealed. The test
mixture then by-passes the test vessel and flows directly into the exhaust system. An ignition is attempted using
the induction spark under quiescent conditions (i.e. after a 6 s to 10 s delay). It is observed whether a flame
detaches from the ignition source (see Annex B).
It is recommended that the ignition testing is carried out without interruption of the production of the test mixture. If
restarting, it will take a finite time to produce a test mixture of constant composition even if the adjustment has not
been changed.
If an ignition is observed, the test substance content in the test mixture is iteratively varied until no further flame
detachment follows. Close to the explosion limits, the incremental change of test substance content is selected so
that it is almost equal to the relative deviation given in Table 1. The test mixture with which a further flame
detachment just fails has to be repeated four times. The determination is terminated when all five tests have taken
place with no observed flame detachment. If flame detachment does occur, the test substance content has to be
further changed, i.e. for determination of the LEL, the test substance content has to be reduced by one increment;
for the UEL, it has to be increased by one increment. Five tests are carried out at the new test substance content.
When it is established that a given test mixture will not ignite, it is recommended that the composition of the non-
ignited test mixture flowing out of the test vessel is measured in order to determine whether any errors have arisen
either with the metering devices or due to leakage.
4.2 Method B ("bomb" method)
4.2.1 Principle
The quiescent test mixture in a closed vessel (the bomb) is subjected to an ignition source. The overpressure given
by the ignition is measured and characterises the explosivity of the test mixture. The amount of test substance in
the test mixture is varied incrementally until the LEL or the UEL is determined, or until it is certain that no explosion
range exists.
4.2.2 Reagents and materials
See 4.1.2.
4.2.3 Apparatus
4.2.3.1 Test vessel.
The test vessel shall be cylindrical or spherical. 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 between 1 and 1,5.
The test vessel and any equipment (valves, ignition source, transducer etc.) fitted to the vessel shall be designed to
withstand a maximum overpressure of at least 15 bar.
The vessel shall be made of stainless steel or any material free of any catalytic effect 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.
If the test mixture is prepared inside the test vessel by partial pressures, it is recommended to disconnect the
pressure measuring system used to prepare the test mixture, via a valve, to protect it during the ignition trials.
The components of the temperature measuring system located inside the test vessel (e.g. thermocouple) have to
be mounted so that propagation of the flame is not hindered.
4.2.3.2 Ignition source.
The ignition source shall be positioned in the centre of the test vessel. Suitable types of ignition source are either a
series of induction sparks or a fuse wire. In the test report, the type of ignition source used shall be stated.
4.2.3.2.1 Induction spark.
See 4.1.3.2.
4.2.3.2.2 Fuse wire.
An electric arc is generated by passing an electric charge along a straight length of fuse wire connected between
two metal rods.
The electrical power required to melt the wire and generate the arc is supplied by an isolating transformer. The
ignition energy delivered by the arc depends on its duration and on the power rating of the isolating transformer.
The energy delivered shall be in the range of 10 J to 20 J as within this range of energies there is no significant
variation in the explosion limits. This is achieved by limiting the power rating of the isolating transformer to between
0,7 kW and 3,5 kW and by the use of a phase control technique. This is a chopping technique that allows only part
of the AC waveform from the transformer secondary windings to energise the wire.
Brass and 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 a NiCr wire (diameter 0,05 mm to
0,2 mm) shall be soldered to the tips of the of the metal rods. The rods shall be positioned in the test vessel so that
the fuse wire is at the centre of the vessel. The electrodes shall be mounted in the vessel such that they are gas
tight at the highest pressures generated during the test. The mounting shall be resistant to heat, resistant to
corrosion from the test mixture and combustion products and shall provide adequate electrical resistance from the
test vessel body.
To reduce the time required for replacing the fusing wire after each test, the rods can be mounted in a plug that can
be screwed into the test vessel wall.

2 2
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 has to be less than 3 mm, additional mechanical support may be
necessary.
4.2.3.3 Explosion overpressure measurement system.
The pressure measurement system consists of:
 a pressure transducer;
 an amplifier;
 recording equipment.
The pressure transducers shall have a resonance frequency greater than 10 kHz.
The pressure measurement system shall have an accuracy that allows the explosion over pressure to be measured
in accordance with the explosion criterion defined in 3.6. It shall have a time resolution of at least 1 ms.
The pressure transducer shall be fitted inside the test vessel, with the head flush with the internal wall.
4.2.3.4 Equipment for preparing the test mixture.
The test mixture can be prepared by partial pressures or mixing together flows of the component substances. This
can be done inside or outside the test vessel.
If the test mixture is prepared by partial pressures, the vessel used for the preparation of the mixture shall be fitted
with:
 a vacuum pump and a vacuum gauge;
 pressure gauges or manometers;
 a means of homogenizing the test mixture (e.g. a stirrer).
The equipment used for measuring and preparing the test mixture has to be designed in such a way that the
uncertainty of measurement of the test substance content in the test mixture is not higher than the data given in
Table 1.
If the test mixture is prepared by mixing flows, 4.1.3.3 and Table 1 apply.
4.2.3.5 Temperature regulating system.
See 4.1.3.4.
4.2.3.6 Safety equipment.
The safety measures specified in Annex D shall be followed.
4.2.4 Preparation of the test mixture
4.2.4.1 General
If liquefied gases or liquids are used, it is necessary to ensure that there is no condensation.
Special care has to be taken when preparing test mixtures from samples of liquid mixtures (4.1.2 and 4.2.2).
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 can be prepared by partial pressures or mixing together flows of the component substances. This
can be done inside or outside the test vessel.
It is also recommended, if possible, to:
 measure the composition of the test mixture;
 check the metering devices;
 ensure that there are no leaks in the mixing system.
4.2.4.2 Preparation of the test mixture by partial pressures
If the preparation of the test mixture involves evacuating the vessel, the amount of air remaining in the vessel has
to be taken into account when calculating the necessary amounts of the flammable materials and air.
The mixture components are sequentially introduced into the vessel to give the required partial pressure. The
partial pressure measuring system shall have a limit deviation 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 need to be evacuated or purged.
NOTE For practical reasons, air is often introduced as the last component, especially if atmospheric air is used.
4.2.4.3 Preparation of the test mixture by mixing flows
The test mixture is prepared by thoroughly mixing metered flows of the gaseous substances.
When liquids are being tested, they shall be totally vaporised before mixing.
It is also recommended, if possible, to:
 measure the composition of the test mixture;
 check the metering devices;
 ensure that there are no leaks in the mixing system.
4.2.5 Procedure
The characterization of explosion limits consists of determining the amount of test substance in the mixture with
which the test mixture no longer ignites (according the explosion criterion in 3.6). Close to the explosion limits, the
incremental change of test substance content is selected such that it is almost equal to the relative uncertainty of
measurement given in Table 1.
The upper or lower explosion limit shall be verified by carrying out four additional tests using the same content of
test substance.
If the explosion limits are determined at elevated temperature, preheat the test vessel and all components carrying
the test mixture to the required temperature. For liquid samples, the temperature of the test mixture shall be at least
25 K higher than the condensation temperature. Prior to each ignition attempt, it has to be ensured that the
temperature in the test vessel differs by not more than 5 K from the required value.
If the test mixture is prepared by the partial pressure method inside the test vessel, the procedure is as follows:
a) preheat the test vessel and associated components to the required temperature;
b) purge the vessel with inert gas (or an inert pre-mixture);
c) evacuate the vessel and measure the residual pressure;
d) charge the test vessel with each substance to the respective partial pressure (it is necessary to take into
account the residual pressure measured beforehand);
e) homogenise (e.g. stir) the mixture for a suitable period (3 min to 5 min);
f) switch off the homogenizer, wait 1 min to 2 min till the mixture is quiescent;
g) close the valve which protects the partial pressure transducer;
h) turn on the explosion overpressure recording system;
i) activate the ignition source and record the pressure-time-curve;
j) return the vessel to atmospheric pressure;
k) repeat steps a) to j) as necessary, changing the mixture composition iteratively (with five tests in total at the
limit concentrations).
It is necessary to ensure that during operations d) and e) chemical decomposition reactions or slow oxidation of the
test mixture do not occur. This is particularly relevant for tests carried out at elevated temperatures. Such reactions
can usually be detected by an increase in pressure and/or temperature, and can lead to false test results.
If the test mixture is prepared by the method of mixing flows, or if it is prepared by partial pressure method in a
vessel separate from the test vessel, the procedure is summarised as follows:
1) preheat the test vessel and associated components to the required temperature;
2) if the test mixture is prepared by mixing flows, purge the test vessel with the test mixture (the volume for
purging has to be at least ten times the vessel volume);
or
if the test mixture is prepared by the partial pressure method using a separate vessel, evacuate the test vessel
to a pressure < 5 mbar and fill with the test mixture;
3) close the test vessel isolation valves;
4) turn on the explosion overpressure recording system;
5) activate the ignition source and record the pressure-time-curve;
6) return the vessel to atmospheric pressure;
7) repeat step 1) to 6) as necessary, changing the mixture composition iteratively (with five tests in total at the
limit concentrations).
For tests on mixtures with high test substance contents, combustion may produce a considerable amount of soot.
In such cases, the interior of the vessel shall be inspected and cleaned to remove build-up of soot prior to
subsequent tests.
4.3 Recording of results
According to this European Standard, all details specified in 4.4 shall be provided. The result has to be expressed
as a molar fraction.
The evaluation of the test is based on the test mixture with which five tests showed that an explosion just failed. For
the uncertainty of measurement, the maximum value of ± 10 % relative or ± 0,2 % absolute permissible according
to this European Standard has to be stated (see 4.1.3.3 and 4.2.3.4). A smaller uncertainty of measurement has to
be stated if it can be derived from the accuracies of the test mixture production. The absolute uncertainty of
measurement is calculated from the relative uncertainty of measurement and the value confirmed by the five tests.
As the measurements are carried out to generate safety data, the results are recorded as follows:
LEL: value confirmed by five tests – absolute deviation.
UEL: value confirmed by five tests + absolute deviation.
In addition, the value for the last ignition has to be stated as it allows the applied step size to be calculated.
NOTE 1 As the values are obtained for safety purposes, for LEL the lowest value respectively for UEL the highest value is
used instead of the mean values.
NOTE 2 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. Such methods 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. Consequently, the details of the apparatus and procedure used
are required to be noted in the test report (see 4.4).
The uncertainty of measurement for the LEL and UEL is essentially determined by the error in the amount of the
test substance in the test mixture (see Table 1) and the size of the incremental change in test substance content.
The verification of the apparatus and procedure shall be done according to Annex F.
4.4 Test report
The test report shall give the following information:
a) reference to this European Standard;
b) laboratory name, operator and date;
c) test conditions: test temperature and ambient pressure;
d) sample identification: composition, purity and source;
e) oxidizer identification:
1) atmospheric or synthetic air;
2) composition, purity and amount of added inert.
f) test apparatus:
1) in the case of method T:
i) preparation of test mixture.
2) in the case of method B:
i) vessel shape and volume;
ii) ignition system;
iii) preparation of test mixture.
g) what was determined (UEL, LEL):
1) the values of the LEL and/or the UEL according to the respective explosion criterion;
2) the uncertainty of measurement of the test substance content in the test mixture;
3) the test substance content in the test mixture closest to the LEL and/or the UEL at which ignition was
observed.
A test mixture is considered non-explosive if, for five tests carried out under the same conditions, the explosive
criterion is not achieved.
An example of an appropriate form that may be used for a test report is given in Annex E.

Annex A
(normative)
Method for determination of the explosion limits of substances that are
difficult to ignite
A.1 Background
This annex specifies the modifications of the tube method which is necessary when determining explosion limits in
air or air/inert mixtures at atmospheric pressure and at temperatures from ambient temperature to 200°C of
substances which are difficult to ignite.
These difficult-to-ignite substances have large quenching distances. They include for example ammonia, amines
and partly halogenated compounds and mixtures containing high proportions of such substances.
The bomb method has been found to be unsuitable for these substances.
A.2 Explanation
A.2.1 Explosion criterion — flame detachment
Because difficult to ignite substances often show no clear flame detachment it is recommended to use a video
camera to record and review the tests for method “T”. Frame by frame analysis may be needed to make a final
decision.
The criterion for an explosion (self-propagating combustion) is the upward movement of the flame from the spark
gap for at least 100 mm. (For examples see Annex B).
Alternatively, if a halo forms it shall reach within 20 mm of the top of a 500 mm tube; this shall also count as an
ignition.
A.2.2 Degree of halogenation
The degree of halogenations is the number of halogen atoms in the molecular structure divided by the number of
H-atoms in the molecular structure.
A.3 Apparatus
A.3.1 Test vessel.
The test vessel is an upright cylindrical test vessel made of glass or another transparent material (e.g.
polycarbonate) with an inner diameter of (80 ± 2) mm and a length of 500 mm. An inlet pipe for the test mixture with
a three-way valve has to be located at the bottom of the tube and an outlet pipe and pressure vent in the upper
part.
The bottom and top of the vessel may be made of other material. Any material used, however, has to be free of
catalytic effects, and special care has to be taken to ensure it is corrosion resistant to the test substance and to the
reaction products which may be HF or HCl.
A.3.2 Reagents and materials.
Special care has to be taken that the chemically inert materials used for gaskets and mountings are resistant to the
reaction products.
The humidity of ai
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