IEC 60079-20-1:2010

IEC 60079-20-1


®

Edition 1.0 2010-01



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Explosive atmospheres –
Part 20-1: Material characteristics for gas and vapour classification – Test
methods and data

Atmosphères explosives –
Partie 20-1: Caractéristiques des substances pour le classement des gaz et des
vapeurs – Méthodes et données d’essai


IEC 60079-20-1:2010

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IEC 60079-20-1


®

Edition 1.0 2010-01



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Explosive atmospheres –
Part 20-1: Material characteristics for gas and vapour classification – Test
methods and data

Atmosphères explosives –
Partie 20-1: Caractéristiques des substances pour le classement des gaz et des
vapeurs – Méthodes et données d’essai


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XC
CODE PRIX
ICS 29.260.20 ISBN 978-2-88910-047-7
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – 60079-20-1 © IEC:2010



CONTENTS

FOREWORD.4


1 Scope.6

2 Normative references .6

3 Terms and definitions .6


4 Classification of gases and vapours.7

4.1 General .7

4.2 Classification according to the maximum experimental safe gaps (MESG).7

4.3 Classification according to the minimum igniting currents (MIC) .8
4.4 Classification according to MESG and MIC.8
4.5 Classification according to a similarity of chemical structure.8
4.6 Classification of mixtures of gases .8
5 Data for flammable gases and vapours, relating to the use of equipment.9
5.1 Determination of the properties .9
5.1.1 General .9
5.1.2 Equipment group .9
5.1.3 Flammable limits .9
5.1.4 Flash point FP .9
5.1.5 Temperature class.10
5.1.6 Minimum igniting current (MIC) .10
5.1.7 Auto-ignition temperature .10
5.2 Properties of particular gases and vapours.10
5.2.1 Coke oven gas .10
5.2.2 Ethyl nitrite .10
5.2.3 MESG of carbon monoxide .10
5.2.4 Methane, Group IIA .11
6 Method of test for the maximum experimental safe gap .11
6.1 Outline of method.11
6.2 Test apparatus .11
6.2.1 General .11
6.2.2 Mechanical strength .12
6.2.3 Interior chamber .12
6.2.4 Exterior chamber .12

6.2.5 Gap adjustment .12
6.2.6 Injection of mixture .12
6.2.7 Source of ignition .12
6.2.8 Materials of test apparatus .12
6.3 Procedure .12
6.3.1 Preparation of gas mixtures .12
6.3.2 Temperature and pressure .12
6.3.3 Gap adjustment .13
6.3.4 Ignition .13
6.3.5 Observation of the ignition process.13
6.4 Determination of maximum experimental safe gap (MESG) .13
6.4.1 Preliminary tests.13
6.4.2 Confirmatory tests .13
6.4.3 Reproducibility of maximum experimental safe gaps.13

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60079-20-1 © IEC:2010 – 3 –


6.4.4 Tabulated values .13

6.5 Verification of the MESG determination method.14

7 Method of test for auto-ignition temperature .14


7.1 Outline of method.14

7.2 Apparatus.14

7.2.1 General .14

7.2.2 Test flask.14

7.2.3 Furnace.15

7.2.4 Thermocouples.15


7.2.5 Sampling syringes or pipettes.15
7.2.6 Timer.15
7.2.7 Mirror .15
7.3 Procedure .15
7.3.1 Sample injection .15
7.3.2 Observations .16
7.3.3 Subsequent tests.16
7.3.4 Confirmatory tests .16
7.4 Auto-ignition temperature .16
7.5 Validity of results.16
7.5.1 Repeatability .16
7.5.2 Reproducibility.16
7.6 Data .17
7.7 Verification of the auto-ignition temperature determination method.17
Annex A (normative) Furnaces of test apparatus for the tests of auto-ignition
temperature .18
Annex B (informative) Tabulated values.26
Bibliography.77

Figure 1 – Test apparatus.11
Figure A.1 – Test apparatus: assembly .19
Figure A.2 – Section A-A (flask omitted) .20
Figure A.3 – Base heater (board made of refractory material) .20
Figure A.4 – Flask guide ring (board made of refractory material) .21
Figure A.5 – Neck heater (board made of refractory material) .22

Figure A.6 – Furnace .23
Figure A.7 – Lid of steel cylinder.24
Figure A.8 – Lid of steel cylinder.25
Figure A.9 – Injection of gaseous sample.25

Table 1 – Classification of temperature class and range of auto-ignition temperatures.10
Table 2 – Values for verification of the apparatus .14
Table 3 – Values for verification of the apparatus .17

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INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________



EXPLOSIVE ATMOSPHERES –



Part 20-1: Material characteristics for gas

and vapour classification –

Test methods and data





FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60079-20-1 has been prepared by IEC technical committee 31:
Equipment for explosive atmospheres.
This first edition of IEC 60079-20-1 cancels and replaces the first edition of IEC 60079-1-
1(2002), the second edition of IEC 60079-4 (1975), its amendment 1(1995) and its
complement: IEC 60079-4A (1970), the first edition of IEC/TR 60079-12 (1978) and the first
edition of IEC 60079-20 (1996). It constitutes a technical revision.

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60079-20-1  IEC:2010 – 5 –


The text of this standard is based on the following documents:

FDIS Report on voting


31/837/FDIS 31/855/RVD



Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.


This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.


A list of all parts of the IEC 60079 series, under the general title: Explosives atmospheres can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

The contents of the corrigendum of July 2012 have been included in this copy.

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– 6 – 60079-20-1 © IEC:2010


EXPLOSIVE ATMOSPHERES –



Part 20-1: Material characteristics for gas

and vapour classification –

Test methods and data








1 Scope

This part of IEC 60079 provides guidance on classification of gases and vapours. It describes
a test method intended for the measurement of the maximum experimental safe gaps (MESG)
1
for gas- or vapour-air mixtures under normal conditions of temperature and pressure so as to
permit the selection of an appropriate group of equipment. The method does not take into
2
account the possible effects of obstacles on the safe gaps . This standard describes also a
test method intended for use in the determination of the auto-ignition temperature of a
chemically pure vapour or gas in air at atmospheric pressure.
The tabulated values of chemical and engineering properties of substances are provided to
assist engineers in their selection of equipment to be used in hazardous areas. It is hoped to
publish further data from time to time, as the results of tests made in several countries
become available.
The scope of these data has been selected with particular reference to the use of equipment
in hazardous areas, and notice has been taken of standard measurement methods.
NOTE 1 The data in this standard have been taken from a number of references which are given in the
bibliography.
NOTE 2 Some variations in the data may appear when references are compared, but usually the discrepancy is
sufficiently small to be of no importance in the selection of equipment.
2 Normative references
The following referenced documents are indispensable for the application 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.
IEC 60079-11, Explosive atmospheres – Part 11: Equipment protection by intrinsic safety "i"

IEC 60079-14, Explosive atmospheres – Part 14: Electrical installations design, selection and
erection
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
—————————
1 An exception is made for substances with vapour pressures which are too low to permit mixtures of the required
concentrations to be prepared at normal ambient temperatures. For these substances, a temperature 5 K above that
needed to give the necessary vapour pressure or 50 K above the flash point is used.
2 The design of the test apparatus for safe gap determination, other than that used for selecting the appropriate group of
enclosure for a particular gas, may need to be different to the one described in this standard. For example, the volume of
the enclosure, flange width, gas concentrations and the distance between the flanges and any external wall or obstruction
may have to be varied. As the design depends on the particular investigation which is to be undertaken, it is impracticable to
recommend specific design requirements, but for most applications the general principles and precautions indicated in the
clauses of this standard will still apply.

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60079-20-1 © IEC:2010 – 7 –


NOTE For the definitions of any other terms, particularly those of a more general nature, reference should be

made to IEC 60050(426) or other appropriate parts of the IEV (International Electrotechnical Vocabulary).

3.1

ignition by hot surface (auto-ignition)

a reaction in the test flask described in 7.2.2 which is evidenced by a clearly perceptible flame

and/or explosion, and for which the ignition delay time does not exceed 5 min


3.2

ignition delay time

the period of time between the introduction of the ignition source and the actual ignition


3.3
auto-ignition temperature
AIT
lowest temperature (of a hot surface) at which under specified test conditions an ignition of a
flammable gas or vapour in mixture with air or air/inert gas occurs
3.4
maximum experimental safe gap
MESG
maximum gap between the two parts of the interior chamber which, under the test conditions
specified below, prevents ignition of the external gas mixture through a 25 mm long flame
path when the internal mixture is ignited, for all concentrations of the tested gas or vapour in
air
3.5
minimum igniting current
MIC
minimum current in resistive or inductive circuits that causes the ignition of the explosive test
mixture in the spark-test apparatus according to IEC 60079-11
4 Classification of gases and vapours
4.1 General
Gases and vapours can be classified according to the group or sub-group of equipment
required for use in the particular gas or vapour atmosphere.
The general principles used to establish the lists of gases and vapours in the table of A nne x B
are given below.

4.2 Classification according to the maximum experimental safe gaps (MESG)
Gases and vapours may be classified according to their maximum experimental safe gaps
(MESG) into the groups I, IIA, IIB and IIC.
NOTE The standard method for determining MESG should be the vessel described in 6.2, but where
determinations have been undertaken only in an 8 l spherical vessel with ignition close to the flange gap these can
be accepted provisionally.
The groups for equipment for explosive gas atmospheres are:
Group I: equipment for mines susceptible to firedamp.
Group II: equipment for places with an explosive gas atmosphere other than mines
susceptible to firedamp.
Group II equipment is subdivided and, for the purpose of classification of gases and vapours,
the MESG limits are:

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Group IIA: MESG ≥ 0,9 mm.

Group IIB: 0,5 mm  MESG  0,9 mm.

Group IIC: MESG  0,5 mm.

NOTE 1 For gases and highly volatile liquids the MESG is determined at 20 °C.


NOTE 2 If it was necessary to do the MESG determination at temperatures higher than ambient temperature a

temperature 5 K above that needed to give the necessary vapour pressure or 50 K above the flash point is used
and this value of MESG is given in the table and the classification of the equipment group is based on this result.


4.3 Classification according to the minimum igniting currents (MIC)


Gases and vapours may be classified according to the ratio of their minimum igniting currents
(MIC) with the ignition current of laboratory methane. The standard method of determining
MIC ratios shall be with the apparatus described in IEC 60079-11, but where determinations
have been undertaken in other apparatus these can be accepted provisionally.
Group II equipment is subdivided and, for the purpose of classification of gases and vapours,
the MIC ratios are:
Group IIA: MIC  0,8.
Group IIB: 0,45  MIC  0,8.
Group IIC: MIC  0,45.
4.4 Classification according to MESG and MIC
For most gases and vapours, it is sufficient to make only one determination of either MESG or
MIC ratio to classify the gas or vapour.
One determination is adequate when:
Group IIA: MESG ≥ 0,9 mm, or MIC  0,9;
Group IIB: 0,55 mm  MESG  0,9 mm, or 0,5  MIC  0,8;
Group IIC: MESG  0,5 mm, or MIC  0,45.
Determination of both the MESG and MIC ratio is required when:
for IIA: 0,8  MIC  0,9 need to confirm by MESG;
for IIB: 0,45  MIC  0,5 need to confirm by MESG;

for IIC: 0,5  MESG  0,55 need to confirm by MIC.
4.5 Classification according to a similarity of chemical structure
When a gas or vapour is a member of an homologous series of compounds, the classification
of the gas or vapour can provisionally be inferred from the data of the other members of the
series with lower molecular weights. However, it is best to run the test if it is possible.
4.6 Classification of mixtures of gases
Mixtures of gases should generally be allocated to a group only after a special determination
of MESG or MIC ratio. One method to estimate the group is to determine the MESG of the
mixture by applying a form of Le Châtelier relationship:

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60079-20-1 © IEC:2010 – 9 –


1

MESG =
mix

⎛ ⎞
X
i
⎜ ⎟
∑
⎜ ⎟
MESG
⎝ i⎠
i


This method should not be applied to mixtures and/or streams that have:

a) acetylene or its equivalent hazard;


b) oxygen or other strong oxidizer as one of the components;

c) large concentrations (over 5 %) of carbon monoxide. Because unrealistically high MESG

values may result, caution should be exercised with two component mixtures where one of

the components is an inert, such as nitrogen.
For mixtures containing an inert such as nitrogen in concentrations less than 5 % by volume,
use an MESG of infinity. For mixtures containing an inert such as nitrogen in concentrations
5 % and greater by volume, use an MESG of 2.
An alternate method that includes stoichiometric ratios is presented in the paper by Brandes
and Redeker.
5 Da
...