Explosive Atmospheres — Part 11: Material Characteristics for Gas and Vapour Classification — Test Methods and Data
1 Scope
This document specifies the test methods and classification rules intended for the measurement of the maximum experimental safe gaps (MESG) for gas-air mixtures or vapour-air mixtures under normal conditions of temperature and pressure (20°C, 101.3 kPa). It provides guidance on classification of gases and vapours. This document gives the characteristic parameters of common flammable gases and vapours so as to permit the selection of an appropriate group of equipment. This document also specifies a test method intended for use in the determination of the auto-ignition temperature (AIT) of a vapour-air mixture or gas-air mixture at atmospheric pressure, so as to permit the selection of an appropriate temperature class of equipment. Values of chemical properties of materials are provided to assist in the selection of equipment to be used in hazardous areas. Further data may be added as the results of validated tests become available.
The materials and the characteristics included in Table B.1 (see Annex B) have been selected with particular reference to the use of equipment in hazardous areas.
The data in this document have been taken from a number of references which are given in the bibliography.
These methods for determining the MESG or the AIT may also be used for gas-air-inert mixtures or vapour-air-inert mixtures. However, data on air-inert mixtures are not tabulated.
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.
ISO 1773 Laboratory glassware - Narrow necked boiling flasks
Note: GB/T 22362-2008 Laboratory glassware — Flasks (ISO 1773:1997, NEQ)
IEC 60050-426 International Electrotechnical Vocabulary - Part 426: Equipment for explosive atmospheres
Note: GB/T 2900.35-2008 Electrotechnical terminology - Equipment for explosive atmospheres (IEC 60050-426:2008, IDT)
IEC 60079-11 Explosive atmospheres - Part 11: Equipment protection by intrinsic safety “i”
Note: GB 3836.4-2021 Explosive atmospheres - Part 4: Equipment protection by intrinsic safety “i” (IEC 60079-11:2011, MOD)
IEC 60079-14 Explosive atmospheres - Part 14: Electrical installations design, selection and erection
Note: GB/T 3836.15-2017 Explosive atmospheres - Part 15: Electrical installations design, selection and erection (IEC 60079-14:2007, MOD)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-426 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: http://www.electropedia.org;
— ISO: http://www.iso.org/obp
3.1
auto-ignition
reaction which is evidenced by a clearly perceptible flame and/or explosion, and for which the ignition delay time does not exceed 5 min
Note: See 7.2.2 for a test method.
3.2
ignition delay time
time between the completed injection of the flammable material and the ignition
3.3
auto-ignition temperature
AIT
lowest temperature (of a surface) at which under specified test conditions an ignition of a flammable gas or vapour in mixture with air or air-inert gas occurs
Note: See 7.2.2 for a test method.
3.4
maximum experimental safe gap
MESG
maximum gap of a joint of 25 mm in width which prevents any transmission of an explosion during tests made under the conditions specified in this document
Note: See Clause 6 for a test method.
3.5
minimum igniting current
MIC
minimum current in a specified test circuit that causes the ignition of the explosive test mixture in the spark test apparatus according to IEC 60079-11
Note: See 5.1.6 for the test circuit.
3.6
flammable limits
lower flammable limit (LFL) and upper flammable limit (UFL) of gas in a gas-air mixture, between which a flammable mixture is formed
Note 1: The term “explosive limits” is used especially in European standardization and regulations interchangeably to describe these limits.
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.6.1
lower flammable limit
LFL
concentration of flammable gas or vapour in air, below which an explosive gas atmosphere does not form
Note 1: For the purposes of Ex Equipment, this was previously referred to as the lower explosive limit (LEL).
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.6.2
upper flammable limit
UFL
concentration of flammable gas or vapour in air, above which an explosive gas atmosphere does not form
Note 1: For the purposes of Ex Equipment, this was previously referred to as the upper explosive limit (UEL).
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.7
equipment grouping
classification system of equipment related to the explosive atmosphere for which they are intended to be used
Note: IEC 60079-0 identifies three equipment groups:
— Group I: equipment for mines susceptible to fire damp;
— Group II: which is sub-divided into groups IIA, IIB and IIC − equipment for all places with an explosive gas atmosphere other than mines susceptible to fire damp;
— Group III: which is sub-divided into groups IIIA, IIIB and IIIC − equipment for all places with an explosive dust atmosphere other than mines susceptible to fire damp.
3.8
flash point
FP
lowest liquid temperature at which, under specified test conditions, a liquid gives off vapours in quantity such as to be capable of forming an ignitable vapour-air mixture
3.9
gas
gaseous phase of a substance that cannot reach equilibrium with its liquid or solid state in the temperature and pressure range of interest
Note: This is a simplification of the scientific definition, and merely requires that the substance is above its boiling point or sublimation point at the ambient temperature and pressure.
3.10
vapour
gaseous phase of a substance that can reach equilibrium with its liquid or solid state in the temperature and pressure range of interest
Note: This is a simplification of the scientific definition, and merely requires that the substance is below its boiling point or sublimation point at the ambient temperature and pressure.
4 Classification of gases and vapours
4.1 General
Group I addresses mines susceptible to firedamp.
Note: Firedamp consists mainly of methane, but always contains small quantities of other gases, such as nitrogen, carbon dioxide, and hydrogen, and sometimes ethane and carbon monoxide. The terms firedamp and methane are used frequently in mining practice as synonyms.
Group II addresses flammable gases and vapours other than in mines susceptible to firedamp. Group II gases and vapours are classified according to their MESG and/or MIC ratio into groups IIA, IIB and IIC.
All flammable materials are classified according to their AIT into temperature classes.
4.2 Classification according to the maximum experimental safe gap (MESG)
Gases and vapours may be classified according to their MESG into Groups IIA, IIB or IIC, based on the determination method described in this document. In order to ensure standardized results the MESG apparatus is dimensioned to avoid the possible effects of obstruction on the safe gaps.
Note 1: The standard method for determining MESG is described in Clause 6. 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.
Note 2: The design of the test apparatus for safe gap determination, other than that used for selecting the appropriate equipment group of enclosure for a particular gas, may need to be different to the one described in this document. 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 this document will still apply.
Note 3: In IEC 60079-14 minimum distances of obstruction from the flameproof flange joints related to the equipment group of the hazardous area are given.
For the purpose of classification, the MESG limits are:
— Group IIA: MESG ≥ 0.90 mm.
— Group IIB: 0.50 mm < MESG < 0.90 mm.
— Group IIC: MESG ≤ 0.50 mm.
Determination of both the MESG and MIC ratio is required when 0.50 < MESG < 0.55. Then the equipment group is determined by MIC ratio.
Note 4: For gases and highly volatile liquids, the MESG is determined at 20°C.
Note 5: 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. The value of MESG is given in Table 1 and the classification of the equipment group is based on this result.
4.3 Classification according to the minimum igniting current ratio (MIC ratio)
Gases and vapours may be classified according to the ratio of their minimum igniting currents (MIC) to the ignition current of laboratory methane into Groups IIA, IIB or IIC. The purity of laboratory methane shall be not less than 99.9% by volume.
Note: The standard method of determining MIC ratios is with the apparatus described in IEC 60079-11, but where determinations have been undertaken in other apparatus these can be accepted provisionally.
For the purpose of classification, the MIC ratios are:
— Group IIA: MIC > 0.80;
Foreword II
Introduction VI
1 Scope
2 Normative references
3 Terms and definitions
4 Classification of gases and vapours
5 Data for flammable gases and vapours, relating to the use of equipment
6 Method of test for the maximum experimental safe gap (MESG)
7 Method of test for auto-ignition temperature (AIT)
Annex A (Normative) Ovens of test apparatus for the tests of auto-ignition temperature
Annex B (Informative) Tabulated values
Annex C (Informative) Determination of cool flames
Annex D (Informative) Volume dependence of auto-ignition temperature
Bibliography
Explosive Atmospheres — Part 11: Material Characteristics for Gas and Vapour Classification — Test Methods and Data
1 Scope
This document specifies the test methods and classification rules intended for the measurement of the maximum experimental safe gaps (MESG) for gas-air mixtures or vapour-air mixtures under normal conditions of temperature and pressure (20°C, 101.3 kPa). It provides guidance on classification of gases and vapours. This document gives the characteristic parameters of common flammable gases and vapours so as to permit the selection of an appropriate group of equipment. This document also specifies a test method intended for use in the determination of the auto-ignition temperature (AIT) of a vapour-air mixture or gas-air mixture at atmospheric pressure, so as to permit the selection of an appropriate temperature class of equipment. Values of chemical properties of materials are provided to assist in the selection of equipment to be used in hazardous areas. Further data may be added as the results of validated tests become available.
The materials and the characteristics included in Table B.1 (see Annex B) have been selected with particular reference to the use of equipment in hazardous areas.
The data in this document have been taken from a number of references which are given in the bibliography.
These methods for determining the MESG or the AIT may also be used for gas-air-inert mixtures or vapour-air-inert mixtures. However, data on air-inert mixtures are not tabulated.
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.
ISO 1773 Laboratory glassware - Narrow necked boiling flasks
Note: GB/T 22362-2008 Laboratory glassware — Flasks (ISO 1773:1997, NEQ)
IEC 60050-426 International Electrotechnical Vocabulary - Part 426: Equipment for explosive atmospheres
Note: GB/T 2900.35-2008 Electrotechnical terminology - Equipment for explosive atmospheres (IEC 60050-426:2008, IDT)
IEC 60079-11 Explosive atmospheres - Part 11: Equipment protection by intrinsic safety “i”
Note: GB 3836.4-2021 Explosive atmospheres - Part 4: Equipment protection by intrinsic safety “i” (IEC 60079-11:2011, MOD)
IEC 60079-14 Explosive atmospheres - Part 14: Electrical installations design, selection and erection
Note: GB/T 3836.15-2017 Explosive atmospheres - Part 15: Electrical installations design, selection and erection (IEC 60079-14:2007, MOD)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-426 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: http://www.electropedia.org;
— ISO: http://www.iso.org/obp
3.1
auto-ignition
reaction which is evidenced by a clearly perceptible flame and/or explosion, and for which the ignition delay time does not exceed 5 min
Note: See 7.2.2 for a test method.
3.2
ignition delay time
time between the completed injection of the flammable material and the ignition
3.3
auto-ignition temperature
AIT
lowest temperature (of a surface) at which under specified test conditions an ignition of a flammable gas or vapour in mixture with air or air-inert gas occurs
Note: See 7.2.2 for a test method.
3.4
maximum experimental safe gap
MESG
maximum gap of a joint of 25 mm in width which prevents any transmission of an explosion during tests made under the conditions specified in this document
Note: See Clause 6 for a test method.
3.5
minimum igniting current
MIC
minimum current in a specified test circuit that causes the ignition of the explosive test mixture in the spark test apparatus according to IEC 60079-11
Note: See 5.1.6 for the test circuit.
3.6
flammable limits
lower flammable limit (LFL) and upper flammable limit (UFL) of gas in a gas-air mixture, between which a flammable mixture is formed
Note 1: The term “explosive limits” is used especially in European standardization and regulations interchangeably to describe these limits.
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.6.1
lower flammable limit
LFL
concentration of flammable gas or vapour in air, below which an explosive gas atmosphere does not form
Note 1: For the purposes of Ex Equipment, this was previously referred to as the lower explosive limit (LEL).
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.6.2
upper flammable limit
UFL
concentration of flammable gas or vapour in air, above which an explosive gas atmosphere does not form
Note 1: For the purposes of Ex Equipment, this was previously referred to as the upper explosive limit (UEL).
Note 2: The concentration can be expressed as either a volume fraction or a mass per unit volume.
3.7
equipment grouping
classification system of equipment related to the explosive atmosphere for which they are intended to be used
Note: IEC 60079-0 identifies three equipment groups:
— Group I: equipment for mines susceptible to fire damp;
— Group II: which is sub-divided into groups IIA, IIB and IIC − equipment for all places with an explosive gas atmosphere other than mines susceptible to fire damp;
— Group III: which is sub-divided into groups IIIA, IIIB and IIIC − equipment for all places with an explosive dust atmosphere other than mines susceptible to fire damp.
3.8
flash point
FP
lowest liquid temperature at which, under specified test conditions, a liquid gives off vapours in quantity such as to be capable of forming an ignitable vapour-air mixture
3.9
gas
gaseous phase of a substance that cannot reach equilibrium with its liquid or solid state in the temperature and pressure range of interest
Note: This is a simplification of the scientific definition, and merely requires that the substance is above its boiling point or sublimation point at the ambient temperature and pressure.
3.10
vapour
gaseous phase of a substance that can reach equilibrium with its liquid or solid state in the temperature and pressure range of interest
Note: This is a simplification of the scientific definition, and merely requires that the substance is below its boiling point or sublimation point at the ambient temperature and pressure.
4 Classification of gases and vapours
4.1 General
Group I addresses mines susceptible to firedamp.
Note: Firedamp consists mainly of methane, but always contains small quantities of other gases, such as nitrogen, carbon dioxide, and hydrogen, and sometimes ethane and carbon monoxide. The terms firedamp and methane are used frequently in mining practice as synonyms.
Group II addresses flammable gases and vapours other than in mines susceptible to firedamp. Group II gases and vapours are classified according to their MESG and/or MIC ratio into groups IIA, IIB and IIC.
All flammable materials are classified according to their AIT into temperature classes.
4.2 Classification according to the maximum experimental safe gap (MESG)
Gases and vapours may be classified according to their MESG into Groups IIA, IIB or IIC, based on the determination method described in this document. In order to ensure standardized results the MESG apparatus is dimensioned to avoid the possible effects of obstruction on the safe gaps.
Note 1: The standard method for determining MESG is described in Clause 6. 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.
Note 2: The design of the test apparatus for safe gap determination, other than that used for selecting the appropriate equipment group of enclosure for a particular gas, may need to be different to the one described in this document. 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 this document will still apply.
Note 3: In IEC 60079-14 minimum distances of obstruction from the flameproof flange joints related to the equipment group of the hazardous area are given.
For the purpose of classification, the MESG limits are:
— Group IIA: MESG ≥ 0.90 mm.
— Group IIB: 0.50 mm < MESG < 0.90 mm.
— Group IIC: MESG ≤ 0.50 mm.
Determination of both the MESG and MIC ratio is required when 0.50 < MESG < 0.55. Then the equipment group is determined by MIC ratio.
Note 4: For gases and highly volatile liquids, the MESG is determined at 20°C.
Note 5: 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. The value of MESG is given in Table 1 and the classification of the equipment group is based on this result.
4.3 Classification according to the minimum igniting current ratio (MIC ratio)
Gases and vapours may be classified according to the ratio of their minimum igniting currents (MIC) to the ignition current of laboratory methane into Groups IIA, IIB or IIC. The purity of laboratory methane shall be not less than 99.9% by volume.
Note: The standard method of determining MIC ratios is with the apparatus described in IEC 60079-11, but where determinations have been undertaken in other apparatus these can be accepted provisionally.
For the purpose of classification, the MIC ratios are:
— Group IIA: MIC > 0.80;
Contents of GB/T 3836.11-2022
Foreword II
Introduction VI
1 Scope
2 Normative references
3 Terms and definitions
4 Classification of gases and vapours
5 Data for flammable gases and vapours, relating to the use of equipment
6 Method of test for the maximum experimental safe gap (MESG)
7 Method of test for auto-ignition temperature (AIT)
Annex A (Normative) Ovens of test apparatus for the tests of auto-ignition temperature
Annex B (Informative) Tabulated values
Annex C (Informative) Determination of cool flames
Annex D (Informative) Volume dependence of auto-ignition temperature
Bibliography
