SIST EN ISO 10156:2018

Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets (ISO 10156:2017)

This document specifies methods for determining whether or not a gas or gas mixture is flammable in
air and whether a gas or gas mixture is more or less oxidizing than air under atmospheric conditions.
This document is intended to be used for the classification of gases and gas mixtures including the
selection of gas cylinder valve outlets.
This document does not cover the safe preparation of these mixtures under pressure and at
temperatures other than ambient.

Gasflaschen - Gase und Gasgemische - Bestimmung der Brennbarkeit und des Oxidationsvermögens zur Auswahl von Ventilausgängen (ISO 10156:2017)

Bouteilles à gaz - Gaz et mélanges de gaz - Détermination du potentiel d'inflammabilité et d'oxydation pour le choix des raccords de sortie de robinets (ISO 10156:2017)

L'ISO 10156:2017 spécifie des méthodes servant à déterminer si un gaz ou un mélange de gaz est ou non inflammable dans l'air et si un gaz ou un mélange de gaz est plus ou moins oxydant que l'air, dans les conditions atmosphériques.
L'ISO 10156:2017 est destiné à être utilisé pour la classification des gaz et des mélanges de gaz, y compris pour le choix des raccords de sortie de robinets de bouteilles à gaz.
L'ISO 10156:2017 ne traite pas de la préparation en toute sécurité de ces mélanges à une pression et à des températures autres que les conditions ambiantes.

Plinske jeklenke - Plini in zmesi plinov - Določitev stopnje vnetljivosti in oksidativnosti za izbiro izhodnega priključka ventila za jeklenko (ISO 10156:2017)

Ta dokument določa metode za ugotavljanje, ali je plin ali plinska zmes vnetljiva v zraku ali ne ter ali je plin oz. plinska zmes bolj ali manj oksidativna od zraka v atmosferskih pogojih.
Ta dokument je predviden za uporabo pri klasifikaciji plinov in plinskih zmesi, vključno z izbiro izhodnih odprtin ventilov plinskih jeklenk.
Ta dokument ne obsega varne priprave teh zmesi pod tlakom in pri temperaturah, ki niso okoljska temperatura.

General Information

• Status: Published
• Public Enquiry End Date: 04-Apr-2016
• Publication Date: 16-Apr-2018
• ICS: 23.020.35 - Gas cylinders
• ICS: 71.100.20 - Gases for industrial application
• Technical Committee: TLP - Pressure vessels
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 27-Feb-2018
• Due Date: 04-May-2018
• Completion Date: 17-Apr-2018
• Directive: 2008/68/EC - Directve 2008/68/EC of the European Parliament and of the council of 24 September 2008 on the inland transport of the dangerous goods
• Mandate: M/086 - Mandate to CEN for standardization in the field of transport of dangerous goods
• Ref Project: EN ISO 10156:2017 - Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets (ISO 10156:2017)

Relations

• Replaces: SIST EN ISO 10156:2010/AC:2010 - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets - Technical Corrigendum 1 (ISO 10156:2010/Cor 1:2010)
• Effective Date: 01-May-2018
• Replaces: SIST EN ISO 10156:2010 - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets (ISO 10156:2010)
• Effective Date: 01-May-2018
• Replaces: SIST EN ISO 10156:2010 - Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets (ISO 10156:2010)
• Effective Date: 08-Jun-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 10156:2018
01-maj-2018
1DGRPHãþD
SIST EN ISO 10156:2010
SIST EN ISO 10156:2010/AC:2010
3OLQVNHMHNOHQNH3OLQLLQ]PHVLSOLQRY'RORþLWHYVWRSQMHYQHWOMLYRVWLLQ

RNVLGDWLYQRVWL]DL]ELURL]KRGQHJDSULNOMXþNDYHQWLOD]DMHNOHQNR,62

Gas cylinders - Gases and gas mixtures - Determination of fire potential and oxidizing

ability for the selection of cylinder valve outlets (ISO 10156:2017)
Gasflaschen - Gase und Gasgemische - Bestimmung der Brennbarkeit und des
Oxidationsvermögens zur Auswahl von Ventilausgängen (ISO 10156:2017)

Bouteilles à gaz - Gaz et mélanges de gaz - Détermination du potentiel d'inflammabilité

et d'oxydation pour le choix des raccords de sortie de robinets (ISO 10156:2017)
Ta slovenski standard je istoveten z: EN ISO 10156:2017
ICS:
23.020.35 Plinske jeklenke Gas cylinders
71.100.20 Industrijski plini Gases for industrial
application
SIST EN ISO 10156:2018 en,fr,de

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

---------------------- Page: 1 ----------------------
SIST EN ISO 10156:2018
---------------------- Page: 2 ----------------------
SIST EN ISO 10156:2018
EN ISO 10156
EUROPEAN STANDARD
NORME EUROPÉENNE
August 2017
EUROPÄISCHE NORM
ICS 23.020.35; 71.100.20 Supersedes EN ISO 10156:2010
English Version
Gas cylinders - Gases and gas mixtures - Determination of
fire potential and oxidizing ability for the selection of
cylinder valve outlets (ISO 10156:2017)

Bouteilles à gaz - Gaz et mélanges de gaz - Gasflaschen - Gase und Gasgemische - Bestimmung der

Détermination du potentiel d'inflammabilité et Brennbarkeit und des Oxidationsvermögens zur

d'oxydation pour le choix des raccords de sortie de Auswahl von Ventilausgängen (ISO 10156:2017)

robinets (ISO 10156:2017)
This European Standard was approved by CEN on 19 August 2017.

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, 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: Avenue Marnix 17, B-1000 Brussels

© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 10156:2017 E

worldwide for CEN national Members.
---------------------- Page: 3 ----------------------
SIST EN ISO 10156:2018
EN ISO 10156:2017 (E)
Contents Page

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

---------------------- Page: 4 ----------------------
SIST EN ISO 10156:2018
EN ISO 10156:2017 (E)
European foreword

This document (EN ISO 10156:2017) has been prepared by Technical Committee ISO/TC 58 “Gas

cylinders” in collaboration with Technical Committee CEN/TC 23 “Transportable gas cylinders” the

secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by February 2018, and conflicting national standards

shall be withdrawn at the latest by February 2018.

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 ISO 10156:2010.

This document has been prepared under a mandate given to CEN by the European Commission and the

European Free Trade Association.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,

France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,

Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
Endorsement notice

The text of ISO 10156:2017 has been approved by CEN as EN ISO 10156:2017 without any modification.

---------------------- Page: 5 ----------------------
SIST EN ISO 10156:2018
---------------------- Page: 6 ----------------------
SIST EN ISO 10156:2018
INTERNATIONAL ISO
STANDARD 10156
Fourth edition
2017-07
Gas cylinders — Gases and gas
mixtures — Determination of fire
potential and oxidizing ability for the
selection of cylinder valve outlets
Bouteilles à gaz — Gaz et mélanges de gaz — Détermination du
potentiel d’inflammabilité et d’oxydation pour le choix des raccords de
sortie de robinets
Reference number
ISO 10156:2017(E)
ISO 2017
---------------------- Page: 7 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form

or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior

written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of

the requester.
ISO copyright office
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2017 – All rights reserved
---------------------- Page: 8 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms, definitions, symbols and units ........................................................................................................................................... 1

4 Flammability of gases and gas mixtures in air ...................................................................................................................... 3

4.1 General ........................................................................................................................................................................................................... 3

4.2 Test method ............................................................................................................................................................................................... 3

4.2.1 Key points concerning safety ................................................................................................................................ 3

4.2.2 Principle .................................................................................................................................................................................. 4

4.2.3 Test apparatus and materials ................................................................................................................................ 4

4.2.4 Procedure for determination of flammability ........................................................................................ 5

4.2.5 Procedure for determination of flammability limits .................. ....................................................... 5

4.2.6 Results for pure gases ........................................................................................................................................... ....... 5

4.3 Calculation method for flammability of gas mixtures containing n flammable gases

and p inert gases .................................................................................................................................................................................... 8

4.4 Examples ...................................................................................................................................................................................................11

4.5 Calculation method for lower flammability limit of gas mixtures ...........................................................12

4.5.1 General...................................................................................................................................................................................12

4.5.2 Mixtures of flammable gases and mixtures of flammable gases with

nitrogen and/or air .....................................................................................................................................................13

4.5.3 Mixtures of flammable gases with inert gases other than nitrogen and air ..............13

4.6 Examples ...................................................................................................................................................................................................13

4.7 Classification according to the Globally Harmonized System (GHS) .....................................................15

5 Oxidizing power of gases and gas mixtures ...........................................................................................................................15

5.1 General ........................................................................................................................................................................................................15

5.2 Test method ............................................................................................................................................................................................15

5.2.1 Key points concerning safety .............................................................................................................................15

5.2.2 Principle ...............................................................................................................................................................................15

5.2.3 Test apparatus .................................................................................................................................................................16

5.2.4 Procedure ............................................................................................................................................................................19

5.2.5 Results ....................................................................................................................................................................................19

5.3 Calculation method ..........................................................................................................................................................................19

5.3.1 Principle ...............................................................................................................................................................................19

5.3.2 C coefficients ...................................................................................................................................................................20

6 Mixtures containing oxygen and flammable gases ........................................................................................................21

6.1 General ........................................................................................................................................................................................................21

6.2 Basis of flammability classification ....................................................................................................................................22

6.3 Examples ...................................................................................................................................................................................................24

Annex A (informative) Classification according to the Globally Harmonized System (GHS) ..................26

Bibliography .............................................................................................................................................................................................................................27

© ISO 2017 – All rights reserved iii
---------------------- Page: 9 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: w w w . i s o .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 58, Gas cylinders, Subcommittee SC 2,

Cylinder fittings.

This fourth edition cancels and replaces the third edition (ISO 10156:2010), which has been technically

revised. It also incorporates ISO 10156:2010/Cor 1:2010.
The main changes compared to the previous edition are as follows:
— 4.1, 4.2.5 and 4.4 have been technically revised;
— 4.5 and 4.6 have been added.
iv © ISO 2017 – All rights reserved
---------------------- Page: 10 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
Introduction

ISO 5145 specifies the dimensions of different cylinder valve outlets for different compatible gas groups.

These compatible gas groups are determined according to practical criteria defined in ISO 14456.

These criteria are based on certain physical, chemical, toxic and corrosive properties of the gases. In

particular, the flammability in air and the oxidizing ability are considered in this document.

One of the potential complications that prompted the development of this document is that while there

are abundant data in the literature relating to pure gases, differences can be found, depending upon the

test methods employed. In the case of gas mixtures, data in the literature are often incomplete or even

non-existent.

The initial aim of this document was to eliminate the ambiguities in the case of differences in the

literature, and above all, to supplement existing data (mainly in the case of gas mixtures).

Subsequently, this document was used for other purposes than the selection of cylinder valve outlets,

such as establishing flammability and oxidizing potential data for the classification and labelling of

gases and gas mixtures.

This document is intended to be used under a variety of national regulatory regimes, but has been

[9]

written so that it is suitable for the application of the UN Model Regulations and the UN-GHS .

© ISO 2017 – All rights reserved v
---------------------- Page: 11 ----------------------
SIST EN ISO 10156:2018
---------------------- Page: 12 ----------------------
SIST EN ISO 10156:2018
INTERNATIONAL STANDARD ISO 10156:2017(E)
Gas cylinders — Gases and gas mixtures — Determination
of fire potential and oxidizing ability for the selection of
cylinder valve outlets
1 Scope

This document specifies methods for determining whether or not a gas or gas mixture is flammable in

air and whether a gas or gas mixture is more or less oxidizing than air under atmospheric conditions.

This document is intended to be used for the classification of gases and gas mixtures including the

selection of gas cylinder valve outlets.

This document does not cover the safe preparation of these mixtures under pressure and at

temperatures other than ambient.
2 Normative references
There are no normative references in this document.
3 Terms, definitions, symbols and units
3.1 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:

— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at http:// www .iso .org/ obp
3.1.1
gas or gas mixture flammable in air

gas or gas mixture that is ignitable in air at atmospheric pressure and a temperature of 20 °C

3.1.2
lower flammability limit in air

minimum content of a gas or gas mixture in a homogeneous mixture with air at which a flame just

starts to propagate

Note 1 to entry: The lower flammability limit is determined at atmospheric conditions.

Note 2 to entry: The term “flammability limit”, as used in this document, is sometimes called “explosion limit”.

3.1.3
upper flammability limit in air

maximum content of a gas or gas mixture in a homogeneous mixture with air at which a flame just

starts to propagate

Note 1 to entry: The upper flammability limit is determined at atmospheric conditions.

Note 2 to entry: The term “flammability limit”, as used in this document, is sometimes called “explosion limit”.

© ISO 2017 – All rights reserved 1
---------------------- Page: 13 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
3.1.4
flammability range
range of concentration between the lower and upper flammability limits

Note 1 to entry: The term “flammability range”, as used in this document, is sometimes also called “explosion range”.

3.1.5
gas or gas mixture more oxidizing than air

gas or gas mixture that is able, at atmospheric pressure, to support the combustion more than a

reference mixture consisting of 23,5 % oxygen in nitrogen
3.1.6
oxidizing power

dimensionless number that compares the oxidizing capability of a gas or gas mixture to that of oxygen

Note 1 to entry: OP is calculated as the sum of the products of the mole fraction(s) of each oxidizing component

times its coefficient of oxygen equivalency, C .
3.1.7
atmospheric conditions
standard pressure of 101,3 kPa at 20 °C
3.2 Symbols
A molar fraction of the i flammable gas in a gas mixture, in %
B molar fraction of the k inert gas in a gas mixture, in %
C coefficient of oxygen equivalency
F i flammable gas in a gas mixture
I k inert gas in a gas mixture
n number of flammable gases in a gas mixture
p number of inert gases in a gas mixture
K coefficient of equivalency of an inert gas relative to nitrogen (see Table 1)
equivalent content of a flammable gas
L lower flammability limit in air of a flammable gas

T maximum content of flammable gas which, when mixed with nitrogen, is not flammable in

air, in %
x molar fraction of the oxidizing component, in %
He helium
Ar argon
Ne neon
Kr krypton
Xe xenon
N nitrogen
2 © ISO 2017 – All rights reserved
---------------------- Page: 14 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
H hydrogen
O oxygen
CO carbon dioxide
SO sulfur dioxide
N O nitrous oxide
SF sulfur hexafluoride
CF carbon tetrafluoride
C F octafluoropropane
3 8
C HF pentafluoroethane
2 5
CH methane
3.3 Units

For the purposes of this document, all gas percentages (%) are given as molar fractions (mol. %) which

are equivalent to volume fractions (vol. %) under normal atmospheric conditions.
4 Flammability of gases and gas mixtures in air
4.1 General

4.2 and 4.3 give a test method and a calculation method for determining whether a gas or gas mixture is

flammable in air. This is used to determine a valve outlet for transportation or GHS classification.

The test method (given in 4.2) may be used in all cases but shall be used when T (or L ) values are not

ci i
available.

The calculation method (given in 4.3) may only be used if reliable T (or L ) values are available.

ci i

4.5 gives a calculation method to determine the lower flammability limit of the flammable mixture

determined in 4.3 and may be used for the GHS flammable gas categories.

In cases where the test result is different from that obtained by calculation, the test result shall take

precedence.

The non-flammable mixtures defined by UN number shall overrule any classification done by

calculation.
4.2 Test method
4.2.1 Key points concerning safety

Tests shall be carried out by trained and competent personnel working in accordance with authorized

procedures (see also 4.2.4). The reaction tube and flowmeter shall be adequately screened to protect

personnel in the event of an explosion. Personnel shall wear personal protective equipment including

safety glasses. During the ignition sequence, the reaction tube shall be open to the atmosphere and

isolated from the gas supply. Care shall also be taken during the analysis of the test gas or mixture.

© ISO 2017 – All rights reserved 3
---------------------- Page: 15 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
4.2.2 Principle

The gas or gas mixture is mixed in the desired proportions with air. In the quiescent test mixture, an

ignition is initiated using an electric spark and it is observed whether or not a flame propagates through

the reaction tube.
4.2.3 Test apparatus and materials
4.2.3.1 General
The apparatus (see Figure 1) includes:
— a mixer;
— a tube in which the reaction takes place;
— an ignition system;
— a system of analysis to determine the test gas composition.

NOTE Alternative equivalent apparatus can be used, as described in standard test methods for the

determination of flammability limits, e.g. EN 1839 and ASTM E681.
4.2.3.2 Preparation
4.2.3.2.1 Test gas

The test gas shall be prepared to represent the most flammable composition that can occur in the

normal course of production. The criteria to be used in establishing the composition of the test gas

are manufacturing tolerances, i.e. the test gas shall contain the highest concentration of flammable

gases encountered in the normal manufacturing process and the moisture content shall be less than or

equal to 0,01 %. The test gas shall be thoroughly mixed and carefully analysed to determine the exact

composition.
4.2.3.2.2 Compressed air

The compressed air shall be analysed and the moisture content shall be less than or equal to 0,01 %.

4.2.3.2.3 Test gas/air mixture

The compressed air and the gas to be tested are mixed in a blender, controlling the flowrates. The air-

flammable gas mixture shall be analysed using a chromatograph or a simple oxygen analyser and a

flammable gas detector.
4.2.3.3 Reaction tube

The test vessel is an upright cylinder of thick glass (e.g. 5 mm) having a minimum inner diameter of

50 mm and a minimum height of 300 mm. The ignition electrodes are separated by a distance of 5 mm

and are placed 50 mm to 60 mm above the bottom of the cylinder. The cylinder is fitted with a pressure-

release opening. The apparatus shall be shielded to restrict any explosion damage.

4.2.3.4 Ignition system

A spark generator capable of supplying high voltage sparks (e.g. 15 kV, 30 mA, a.c.) with energy of 10 J

shall be used. The spark gap (distance between the electrodes) shall be 5 mm, the spark duration 0,2 s

to 0,5 s.
4 © ISO 2017 – All rights reserved
---------------------- Page: 16 ----------------------
SIST EN ISO 10156:2018
ISO 10156:2017(E)
4.2.4 Procedure for determination of flammability

When carrying out flammability tests, care shall be taken to avoid explosion. This can be done by

commencing the experimental work at a known “safe” concentration of 1 % test gas in air. Subsequently,

the initial gas concentration can be increased in small steps by 1 % until ignition occurs.

Prior to each ignition attempt, the test vessel shall be purged with the test mixture. The purging volume

shall be at least 10 times the volume of the test vessel. Then, an ignition is attempted with the induction

spark when the test mixture is quiescent, and it is observed visually whether or not a flame detaches

from the ignition source and propagates.

If a flame detachment and an upwards propagation of at least 100 mm is observed, the test substance

shall be classified as flammable.

If the chemical structure of the gas indicates that it would be non-flammable and the composition of the

stoichiometric mixture with air can be calculated, only mixtures in the range from 10 % (absolute) less

than the stoichiometric composition to 10 % greater than this composition need to be tested in 1 % steps.

With mixtures containing hydrogen, the flame is almost colourless. In order to confirm the presence of

such flames, the use of temperature-measuring probes is recommended [see Figure 1 a)].

4.2.5 Procedure for determination of flammability limits

Unlike at the determination of flammability in general, it is necessary to apply a different test procedure

for determining flammability limits (FL). Using the same test apparatus, test gas preparation and

criterion of ignition as described in 4.2.3 and 4.2.4, the characterization of flammability limits consists

of determining the amount of test substance in air with which the test mixture no longer ignites. Close

to the flammability limit, the incremental change of test substance content in air is selected such that it

is almost 0,1 % by volume for FL < 10 % and 0,2 % by volume for FL ≥ 10 %.

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.

Prior to each ignition attempt, the test vessel is purged with the test mixture. The purging volume shall

be at least 10 times the volume of the test vessel. When purging is complete, the inlet to the test vessel

is sealed. The test mixture then bypasses the test vessel and flows directly into the exhaust system. An

ignition is attempted using the induction spark under quiescent conditions. It is observed whether or

not a flame detaches from the ignition source and propagates at least 100 mm.

If an ignition is observed, the test gas content in the test mixture is iteratively varied until no further

flame detachment follows. The test mixture concentration at which an ignition just fails (just no flame

detachment) shall be confirmed with four additional tests. The determination is terminated when with

all five tests a flame detachment is not observed. If flame detachment does occur, the test gas content

shall be further changed and the test gas content shall be reduced (lower flammability limit) or to be

increased (upper flammability limit) by one increment. Again, the tests are carried out at the new test

substance content.

The flammability limit is the test gas concentration in mixture with air at which an ignition just fails.

4.2.6 Results for pure gases

A list of flammable gases is given in Table 2 together with T values and L values. These values have

ci i
been obta
...