prEN 17624

Determination of explosion limits of gases and vapours at elevated pressures, elevated temperatures or with oxidizers other than air

This document specifies a test method to determine the explosion limits of gases, vapours and their mixtures, mixed with a gaseous oxidizer or an oxidizer/inert gas mixture at pressures from 1 bar to 100 bar and for temperatures up to 400 °C.

Bestimmung der Explosionsgrenzen von Gasen und Dämpfen bei erhöhten Drücken, erhöhten Temperaturen oder mit Oxidationsmitteln, welche nicht aus Luft bestehen

Dieses Dokument legt ein Prüfverfahren zur Bestimmung der Explosionsgrenzen von Gasen, Dämpfen und deren Gemischen, gemischt mit einem gasförmigen Oxidator oder einem Oxidator-Inertgas-Gemisch, bei Drücken von 1 bar bis 100 bar und für Temperaturen bis 400 °C fest.

Détermination des limites d'explosivité des gaz et vapeurs à pressions et températures élevées avec des oxydants autres que l’air

Le présent document spécifie une méthode d’essai pour déterminer les limites d’explosivité de gaz, de vapeurs et de leurs mélanges, associés à un oxydant gazeux ou à un mélange oxydant/gaz inerte, à des pressions allant de 1 bar à 100 bar et à des températures pouvant atteindre 400 °C.

Določanje eksplozijskih mej plinov in hlapov pri povišanem tlaku, povišani temperaturi ali z oksidanti, ki niso sestavljeni iz zraka

General Information

• Status: Not Published
• ICS: 13.230 - Explosion protection
• Technical Committee: CEN/TC 305 - Potentially explosive atmospheres - Explosion prevention and protection
• Drafting Committee: CEN/TC 305/WG 1 - Test methods for determining the flammability characteristics of substances (provisional title)
• Current Stage: 4599 - Dispatch of FV draft to CMC - Finalization for Vote
• Due Date: 13-Sep-2021
• Completion Date: 13-Sep-2021
• Directive: 2006/42/EC - Directive 2006/42/EC of the European Parliament and of the Council of 17 May 2006 on machinery, and amending Directive 95/16/EC (recast)
• Directive: 2014/34/EU - Directive 2014/34/EU Of The European Parliament And Of The Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to equipment and protective systems intended for use in potentially explosive atmospheres (recast)
• Mandate: M/396 - Mandate to CEN and Cenelec for standardisation in the field of machinery
• Mandate: M/BC/CEN/92/46 - Standardization mandate assigned to CEN/CENELEC concerning equipment and protective systems intended for use in potentially explosive atmospheres
• Ref Project: oSIST prEN 17624:2021 - Determination of explosion limits of gases and vapours at elevated pressures, elevated temperatures or with oxidizers other than air

Standards Content (sample)

SLOVENSKI STANDARD
oSIST prEN 17624:2021
01-januar-2021
Določanje eksplozijskih mej plinov in hlapov pri povišanem tlaku, povišani
temperaturi ali z oksidanti, ki niso sestavljeni iz zraka

Determination of explosion limits of gases and vapours at elevated pressures, elevated

temperatures or with oxidizers other than air
Bestimmung der Explosionsgrenzen von Gasen und Dämpfen bei erhöhten Drücken,
erhöhten Temperaturen oder mit Oxidationsmitteln, welche nicht aus Luft bestehen

Détermination des limites d'explosivité des gaz et vapeurs à pressions et températures

élevées avec des oxydants autres que l’air
Ta slovenski standard je istoveten z: prEN 17624
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
oSIST prEN 17624:2021 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN 17624:2021
DRAFT
EUROPEAN STANDARD
prEN 17624
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2020
ICS 13.230
English Version
Determination of explosion limits of gases and vapours at
elevated pressures, elevated temperatures or with
oxidizers other than air

Détermination des limites d'explosivité des gaz et Bestimmung der Explosionsgrenzen von Gasen und

vapeurs à pressions et températures élevées avec des Dämpfen bei erhöhten Drücken, erhöhten

oxydants autres que l'air Temperaturen oder mit Oxidationsmitteln, welche
nicht aus Luft bestehen

This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee

CEN/TC 305.

If this draft becomes a European Standard, 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.

This draft European Standard was established by CEN 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.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of which they are

aware and to provide supporting documentation.

Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without

notice and shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 17624:2020 E

worldwide for CEN national Members.
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Contents Page

European foreword ....................................................................................................................................................... 3

Introduction .................................................................................................................................................................... 4

1 Scope .................................................................................................................................................................... 5

2 Normative references .................................................................................................................................... 5

3 Terms and definitions ................................................................................................................................... 5

4 Test methods .................................................................................................................................................... 6

4.1 General ................................................................................................................................................................ 6

4.2 Reagents and materials ................................................................................................................................. 7

4.2.1 Sample ................................................................................................................................................................. 7

4.2.2 Oxidizer............................................................................................................................................................... 7

4.2.3 Inert gases .......................................................................................................................................................... 7

4.2.4 Gaskets and mountings ................................................................................................................................. 7

4.3 Apparatus ........................................................................................................................................................... 7

4.3.1 Test vessel .......................................................................................................................................................... 7

4.3.2 Measurement system to adjust the initial pressure and temperature ........................................ 8

4.3.2.1 Initial pressure ........................................................................................................................................ 8

4.3.2.2 Initial temperature................................................................................................................................. 8

4.3.2.3 Explosion overpressure measurement system ............................................................................ 8

4.3.2.4 Measurement system to measure the temperature rise .......................................................... 9

4.3.3 Ignition source ................................................................................................................................................. 9

4.3.3.1 Induction spark ....................................................................................................................................... 9

4.3.3.2 Surface-gap spark ................................................................................................................................... 9

4.3.3.3 Exploding wire ...................................................................................................................................... 10

4.3.4 Equipment for preparing the test mixture ......................................................................................... 10

4.3.5 Temperature regulating system ............................................................................................................. 11

4.3.6 Safety equipment.......................................................................................................................................... 12

4.4 Preparation of the test mixture .............................................................................................................. 12

4.4.1 General ............................................................................................................................................................. 12

4.4.2 Preparation of the test mixture .............................................................................................................. 12

4.5 Procedure........................................................................................................................................................ 12

4.6 Recording of results .................................................................................................................................... 13

5 Verification ..................................................................................................................................................... 14

6 Test report ...................................................................................................................................................... 14

Annex A (normative) Safety measures ................................................................................................................ 15

Annex B (normative) Verification ......................................................................................................................... 16

Annex ZA (informative) Relationship between this European Standard and the essential

requirements of Directive2006/42/EC aimed to be covered ...................................................... 18

Bibliography ................................................................................................................................................................. 19

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European foreword

This document (prEN 17624:2020) 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 document is currently submitted to the CEN Enquiry.

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) 2006/42/EC.

For relationship with EU Directive 2006/42/EC, see informative Annex ZA, which is an integral part of

this document.
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Introduction
In accordance with EN ISO 12100:2010, this is a type B standard.

The scope of EC Directive 2014/34 (ATEX) deals with explosive atmospheres of mixtures of flammable

substances and air in the pressures range between 0,8 kPa and 1,1 kPa and the temperature range

between −20 °C and 60 °C (atmospheric conditions). Therefore, the scope of the standards dealing with

the determination of safety characteristic data, for which CEN gave a mandate with respect to EU

Directive 2014/34 (ATEX), covers in general only such pressure and temperature conditions, and air as

the only oxidizer.

Technical conditions in plants etc. may differ remarkably from the pressure and temperature range of

the ATEX. Furthermore, explosive mixtures of flammable substances and oxidizers other than air are

likely to occur.

Safety characteristic data may, however, depend remarkably on both pressure and temperature, and

also the oxidizer.

The hazard of an explosion can be avoided by preventing the formation of explosive mixtures of gases

and/or vapours with oxidizers. To do so, the explosion limits (also known as “flammability limits) of the

flammable substance at the respective non-atmospheric conditions need to be known.

To obtain reliable and comparable results it is necessary to standardize the conditions for determining

the explosion limits at non-atmospheric conditions.
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1 Scope

This document specifies a test method to determine the explosion limits of gases, vapours and their

mixtures, mixed with a gaseous oxidizer or an oxidizer/inert gas mixture at pressures from 1 bar to

100 bar and for temperatures up to 400 °C.
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.

ISO 10156:2017, Gas cylinders — Gases and gas mixtures — Determination of fire potential and oxidizing

ability for the selection of cylinder valve outlets
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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 http://www.electropedia.org/
3.1
flammable substance

substance in the form of gas, vapour or mixtures of these, able to undergo an explosive exothermic

reaction with an oxidizer or an oxidizer/inert gas mixture when ignited
[SOURCE: EN 13237:2012, 3.37, modified]
3.2
explosion range

range of the concentration of a flammable substance or mixture of substances with an oxidizer, within

which an explosion can occur determined under specified test conditions
Note 1 to entry: The explosion limits are not part of the explosion range.
[SOURCE: EN 13237:2012, 3.22, modified]
3.3
lower explosion limit
LEL
lowest concentration of the explosion range

Note 1 to entry: Those concentrations are given at which an explosion just fails during the tests.

[SOURCE: EN 13237:2012, 3.19.1, modified]
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3.4
upper explosion limit
UEL
highest concentration of the explosion range

Note 1 to entry: Those concentrations are given at which an explosion just fails during the tests.

[SOURCE: EN 13237:2012, 3.19.2, modified]
3.5
inert gas
gas that does not react with the test substance or oxidizer
3.6
explosion criterion

either an explosion pressure p relative to the initial pressure (p ) as follows (considering the

ex i
overpressure that is created by the ignition source alone (p )):
p /p ≥ (1,05 + p /p − 1) for initial pressures p ≤ 2)
ex i IS i i
p /p ≥ (1,02 + p /p − 1) (for initial pressures p > 2)
ex i IS i i
or a temperature rise (ΔT) of at least 100 K
3.7
oxidizer

any oxidising gas except highly reactive oxidisers with oxidizing potentials according to

EN ISO 10156:2017 higher than oxygen, e.g. ozone, fluorine, fluorinated compounds etc.

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 or air/inert gas
4 Test methods
4.1 General

The determination consists of a series of ignition tests which are carried out with test mixtures varying

the test substance content.

The quiescent test mixture in the closed vessel is subjected to an ignition source. The overpressure and

the temperature rise as a result of the ignition is measured and characterizes 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 ascertained that there is no explosion range.
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When it is established that a given test mixture will not ignite, it is recommended to analyse the

quantitative composition of the non-ignited test mixture flowing out of the test vessel in order to ensure

that no errors occurred either with the metering devices, or due to leakage.

NOTE 1 For organic substances consisting exclusively of carbon, hydrogen and oxygen (with the exception of

peroxides), the starting composition of the mixture to determine the LEL in air and oxygen can be roughly

estimated. For other oxidizers there is currently no estimation method available.

NOTE 2 At 20 °C, the LEL in air, in many cases, is approximately half the test substance content of the

stoichiometric composition in air. At 20 °C, the LEL in oxygen is similar to that in air. The temperature

dependence of the LEL has to be taken into account. Up to 200 °C resp. up to temperatures near to the auto-

ignition temperature, the LEL in air and oxygen decreases more or less linearly up to 50 % of the value estimated

for 20 °C.

NOTE 3 Currently, neither for ambient conditions, nor for non-ambient conditions is there a method available

for readily estimating the UEL. However, the UEL rises remarkably with increasing temperature, increasing

pressure or oxidizing potential of the oxidizer.
4.2 Reagents and materials
4.2.1 Sample

The sample is 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, its composition (including the scatter) shall be stated in the test report. In the case of a

process sample of unknown composition, the sample shall be defined as precisely as is possible e.g. by

process conditions.

Sample containers shall be kept closed before and after sampling to avoid changes in the sample

composition (e.g. loss of volatile components from mixtures).
4.2.2 Oxidizer

The oxidizer shall be free of water (≤0,1 mol% water vapour absolute) and oil (≤0,1 g/m oil).

If synthetic air is used, it shall be stated in the report.
4.2.3 Inert gases

The purity of the inert gas or the mixture of inert gases, shall be 99,8 mol%, or better.

If a mixture of inert gases is used, the composition of the mixture shall be stated in the test report.

4.2.4 Gaskets and mountings

In oxygen enriched mixtures it is absolutely necessary to take care that the materials of the gaskets and

mountings are not of organic origin and that they are oil and grease free to avoid accidents.

Special care shall be taken in the case of corrosive oxidizers or corrosive flammable substances.

4.3 Apparatus
4.3.1 Test vessel

The test vessel shall be cylindrical or spherical. If a cylindrical vessel is used, the length to diameter

ratio shall be between 1,0 and 1,5. The minimum internal volume of the test vessel depends on the

initial pressure in the tests and shall be according to the following Table 1.
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Table 1 — Fundamental requirements of the apparatus
Minimum internal volume of
Initial Pressure (p )
Ignition source
the test vessel
exploding wire
10 dm
1 bar ≤ p < 5 bar
induction spark, surface-gap spark
5 dm
surface-gap spark up to 25 bar,
5 bar ≤ p < 50 bar 3
i 3 dm
exploding wire
p ≥ 50 bar 3
exploding wire
i 1 dm

The test vessel and any equipment (valves, ignition source, pressure and temperature sensors etc.)

fitted to the vessel shall be designed to withstand a maximum overpressure of at least 15 times the

initial pressure if air is the oxidizer. For mixtures with an oxidizer having an oxidizing potential

according to EN ISO 10156:2017 higher than air, the test vessel and the equipment shall be designed to

withstand a maximum overpressure of at least 30 times the initial pressure.

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. It has to be grounded.

The test vessel shall be equipped with sufficient ports to allow filling, evacuating and purging.

It has to be equipped with an ignition source, a temperature and pressure measuring system to set the

initial pressure and temperature and a temperature and pressure measuring system to measure the

generated temperature rise and overpressure after ignition.
4.3.2 Measurement system to adjust the initial pressure and temperature
4.3.2.1 Initial pressure

The pressure measuring system may contain a piezoresistive pressure transducer. If the test mixture is

prepared inside the test vessel by partial pressures using this pressure transducer then it shall be

calibrated. It is recommended that this pressure measuring system is disconnected, via a valve to

protect it, during the ignition trials.
4.3.2.2 Initial temperature

The temperature measuring system consists of a sheath thermocouple and recording equipment. The

thermocouple shall have a limit deviation of not more than 1,5 K. The diameter of the thermocouple

shall not exceed 1,5 mm. It is recommended that the diameter of this thermocouple is larger than that of

the thermocouple used to detect the temperature rise because comparison of the starting temperature

with both temperature measuring systems may indicate any fault of the temperature measuring system

to measure the generated temperature rise.
4.3.2.3 Explosion overpressure measurement system

The pressure measuring system for detecting the overpressure after ignition shall contain a

piezoelectric or piezoresistive pressure transducer. If the head of the pressure transducers is not flush

to the internal wall the maximum distance between the head of the pressure transducer and inner

surface shall be 100 mm.
The pressure transducers shall have a resonance frequency greater than 30 kHz.
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The pressure measurement system shall have an accuracy that allows the explosion overpressure to be

measured in accordance with the explosion criterion (see 3.6). It shall have a resolution of at least 10

of full scale.
4.3.2.4 Measurement system to measure the temperature rise

The temperature measuring system consists of a sheath thermocouple and recording equipment. The

thermocouple shall be mounted inside the vessel above the ignition source with a distance of

10 mm ± 1 mm from the top of the vessel. Its diameter shall be 0,5 mm.

By comparison of the starting temperature with both temperature measuring systems any fault of the

temperature measuring system to measure the generated temperature rise can be detected.

4.3.3 Ignition source

The ignition source shall be positioned above the bottom of the test vessel. Suitable types of an ignition

source are either a series of induction sparks, a surface gap spark or an exploding wire. In the test

report, the type of ignition source used shall be stated.
4.3.3.1 Induction spark
This ignition source may be used for initial pressures up to 5 bar.

A series of induction sparks between two electrodes is used as the ignition source.

The electrodes shall end (50 ± 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 3,0 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 an arrangement

gives a power of approximately 10 W.

Fluorinated substances, e.g. SF6, CF4 etc., can suppress induction sparks. In such cases an ignition

source according to 4.3.3.2 or 4.3.3.3 shall apply.
4.3.3.2 Surface-gap spark
This ignition source may be used for initial pressures up to 25 bar.

An electric arc which is generated by passing an electric charge along the straight length of a graphite

rod connected between two metal rods is used as the ignition source.
The metal rods shall end (50 ± 1) mm above the bottom of the test vessel.

The electrical power necessary to generate the arc is supplied by a capacitive discharge or an isolating

transformer. If the arc is generated by using capacitive discharge the ignition energy delivered by the

arc depends on the capacity and charging voltage.
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The energy delivered shall be in the range of 10 J to 20 J as within this range there is no significant

influence onto the results. Ten J to 20 J are achieved by adjusting the capacity to about 220 μF and the

charging voltage to about 440 V.

Stainless steel is a suitable material for the rods. The rods having a diameter between 3,0 mm and

4,0 mm shall be parallel to each other with a separation distance of (6 ± 1) mm. The graphite rod having

a diameter of (2 ± 0,2) mm shall be fixed between the metal rods at their end. 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.

The cross-section of the wires connecting the power supply to the rods shall be between 2,5 mm and

7,0 mm . The length of the wires shall be less than 10 m.
4.3.3.3 Exploding wire

This ignition source may be used for initial pressures up to 100 bar (see Table 1).

An electric arc is generated by passing an electric charge along a straight length of exploding wire

connected between two metal rods.
The metal rods shall end (50 ± 1) mm above the bottom of the test vessel.

The electrical power required to melt the wire and generate the arc is supplied by an isolating

transformer or a capacitor with an inductor. The ignition energy delivered by the arc depends on its

duration and on the power rating of the isolating transformer or on capacity and voltage of the

capacitor respectively. The energy delivered shall be in the range of 10 J to 20 J as within this range

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 energize the wire. If a capacitor is used, a capacity of 470 μF and a charging voltage up to

450 V is sufficient. The inductor should have an inductance of about 5 mH and copper wire of a

diameter equal or greater than 2,0 mm. The ignition energy can be determined by measuring current

and voltage of the electric arc. The voltage should be measured directly at the igniter and the current via

a shunt with a sampling rate of at least 10 kHz. If necessary, the energy can be reduced by reducing the

charging voltage.

Brass and stainless steel are suitable materials for the rods. The rods shall be parallel to each other with

a separation distance of (5,0 ± 1,0) 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 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.

The cross-section of the wires connecting the transformer to the rods shall be between 2,5 mm and

7,0 mm . The length of the wires shall be less than 5 m. The diameter of the rods shall be between

3,0 mm and 4,0 mm.
4.3.4 Equipment for preparing the test mixture
It is recommended to prepare the test mixture by partial pressures.

In case all components of the mixtures to test are gaseous this can be done inside or outside the test

vessel.

In this case the vessel used for the preparation of the mixture shall be fitted with:

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— a vacuum pump and a vacuum gauge;
— a pressure measuring system to measure the partial pressures;
— a means of homogenizing the test mixture (e.g. a stirrer).

The pressure measuring system used to measure the partial pressures shall have a limit deviation

which corresponds to half of the incremental change of test substance content mentioned in 4.5 or

better. Especially when initial pressures higher than 25 bar are used it is recommended to prepare the

mixture outside the explosion vessel at a pressure lower than the necessary initial pressure and to fill

the explosion vessel using a compressor.

In case the flammable components of the mixtures to test are liquid at ambient conditions it is

recommended to prepare the respective mixture inside the test vessel.
In this case the test vessel s
...