GB/T 12476.3-2017 Electrical apparatus for use in the presence of combustible dust—Part 3: Classification of areas where combustible dusts are or may be present (English Version)
1 Scope
This part specifies the identification and classification of areas where explosive dust atmospheres and combustible dust layers are present, in order to permit the proper assessment of ignition sources in such areas.
In this part, explosive dust atmospheres and combustible dust layers are treated separately. In Clause 4, area classification for explosive dusts clouds is described, with dust layers acting as one of the possible sources of release. In Clause 7, the hazard of dust layer ignition is described.
The examples in this part are based on a system of effective housekeeping being implemented in the plant to prevent dust layers from accumulating. Where effective housekeeping is not present, the area classification includes the possible formation of explosive dust clouds from dust layers.
The principles of this part can also be followed when combustible fibres or flyings may cause a hazard.
This part is intended to be applied where there can be a risk due to the presence of explosive dust atmospheres or combustible dust layers under normal atmospheric conditions.
This part does not apply to:
— underground mining areas;
— areas where a risk can arise due to the presence of hybrid mixtures;
— dusts of explosives that do not require atmospheric oxygen for combustion, or to pyrophoric substances;
— catastrophic failures which are beyond the concept of abnormality dealt with in this part (see Note 1);
— any risk arising from an emission of flammable or toxic gas from the dust.
This part does not take into account the effects of consequential damage following a fire or an explosion.
Note 1: Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a pneumatic conveyor.
Note 2: In any process plant, irrespective of size, there can be numerous sources of ignition apart from those associated with equipment. Appropriate precautions will be necessary to ensure safety in this context, but these are outside the scope of this part.
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.
GB 3836.1-2010 Explosive Atmospheres — Part 1: Equipment — General Requirements (IEC 60079-0: 2007, MOD)
GB 12476.1-2013 Electrical Apparatus for Use in the Presence of Combustible Dust — Part 1: General Requirements (IEC 61241-0: 2004, MOD)
ISO/IEC 80079-20-2 Explosive Atmospheres — Part 20-2: Material Characteristics — Combustible Dusts Test Methods
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB 3836.1-2010 and GB 12476.1-2013 and the following apply.
Note: Additional definitions applicable to explosive atmospheres can be found in GB/T 2900.35-2008.
3.1
area
three-dimensional region or space
3.2
atmospheric conditions (surrounding conditions)
conditions that include variations in pressure and temperature above and below reference levels of 101.3 kPa (1 013 mbar) and 20 °C (293 K), provided that the variations have a negligible effect on the explosive properties of the combustible dust
3.3
hybrid mixture
mixture of flammable substances in different physical states, with air
Note: An example of a hybrid mixture is a mixture of methane, coal dust and air.
3.4
dust
generic term including both combustible dust and combustible flyings
3.5
combustible dust
finely divided solid particles, 500 μm or less in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures
Note 1: This definition may also include dust and grit as defined in HJ 492.
Note 2: The term ‘solid particle’ is intended to address particles in the solid phase and not the gaseous or liquid phase, but does not preclude a hollow particle.
3.6
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust, or flyings in which, after ignition, permits self-sustaining flame propagation
3.7
conductive dust
combustible dust with electrical resistivity equal to or less than 103 Ω•m
3.8
non-conductive dust
combustible dust with electrical resistivity greater than 103 Ω•m
3.9
combustible flyings
solid particles, including fibres, greater than 500 μm in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures
Note: Examples of fibres and flyings include rayon, cotton (including cotton linters and cotton waste), sisal, jute, hemp, cocoa fibre, oakum, and baled waste kapok.
Foreword II
Introduction IV
1 Scope
2 Normative References
3 Terms and Definitions
4 Area Classification
5 Sources of Release
6 Zones
7 Dust Layer Hazard
8 Documentation
Annex A (Informative) Area Classification Application
Annex B (Informative) Risk of Fire from Hot Surface Ignition of Dust Layer
Annex C (Informative) Housekeeping
Annex D (Informative) Introduction of an Alternative Risk Assessment Method Encompassing ‘Equipment Protection Levels’ for Ex Equipment
Bibliography
GB/T 12476.3-2017 Electrical apparatus for use in the presence of combustible dust—Part 3: Classification of areas where combustible dusts are or may be present (English Version)
Standard No.
GB/T 12476.3-2017
Status
superseded
Language
English
File Format
PDF
Word Count
12500 words
Price(USD)
370.0
Implemented on
2018-7-1
Delivery
via email in 1 business day
Detail of GB/T 12476.3-2017
Standard No.
GB/T 12476.3-2017
English Name
Electrical apparatus for use in the presence of combustible dust—Part 3: Classification of areas where combustible dusts are or may be present
1 Scope
This part specifies the identification and classification of areas where explosive dust atmospheres and combustible dust layers are present, in order to permit the proper assessment of ignition sources in such areas.
In this part, explosive dust atmospheres and combustible dust layers are treated separately. In Clause 4, area classification for explosive dusts clouds is described, with dust layers acting as one of the possible sources of release. In Clause 7, the hazard of dust layer ignition is described.
The examples in this part are based on a system of effective housekeeping being implemented in the plant to prevent dust layers from accumulating. Where effective housekeeping is not present, the area classification includes the possible formation of explosive dust clouds from dust layers.
The principles of this part can also be followed when combustible fibres or flyings may cause a hazard.
This part is intended to be applied where there can be a risk due to the presence of explosive dust atmospheres or combustible dust layers under normal atmospheric conditions.
This part does not apply to:
— underground mining areas;
— areas where a risk can arise due to the presence of hybrid mixtures;
— dusts of explosives that do not require atmospheric oxygen for combustion, or to pyrophoric substances;
— catastrophic failures which are beyond the concept of abnormality dealt with in this part (see Note 1);
— any risk arising from an emission of flammable or toxic gas from the dust.
This part does not take into account the effects of consequential damage following a fire or an explosion.
Note 1: Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a pneumatic conveyor.
Note 2: In any process plant, irrespective of size, there can be numerous sources of ignition apart from those associated with equipment. Appropriate precautions will be necessary to ensure safety in this context, but these are outside the scope of this part.
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.
GB 3836.1-2010 Explosive Atmospheres — Part 1: Equipment — General Requirements (IEC 60079-0: 2007, MOD)
GB 12476.1-2013 Electrical Apparatus for Use in the Presence of Combustible Dust — Part 1: General Requirements (IEC 61241-0: 2004, MOD)
ISO/IEC 80079-20-2 Explosive Atmospheres — Part 20-2: Material Characteristics — Combustible Dusts Test Methods
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB 3836.1-2010 and GB 12476.1-2013 and the following apply.
Note: Additional definitions applicable to explosive atmospheres can be found in GB/T 2900.35-2008.
3.1
area
three-dimensional region or space
3.2
atmospheric conditions (surrounding conditions)
conditions that include variations in pressure and temperature above and below reference levels of 101.3 kPa (1 013 mbar) and 20 °C (293 K), provided that the variations have a negligible effect on the explosive properties of the combustible dust
3.3
hybrid mixture
mixture of flammable substances in different physical states, with air
Note: An example of a hybrid mixture is a mixture of methane, coal dust and air.
3.4
dust
generic term including both combustible dust and combustible flyings
3.5
combustible dust
finely divided solid particles, 500 μm or less in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures
Note 1: This definition may also include dust and grit as defined in HJ 492.
Note 2: The term ‘solid particle’ is intended to address particles in the solid phase and not the gaseous or liquid phase, but does not preclude a hollow particle.
3.6
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust, or flyings in which, after ignition, permits self-sustaining flame propagation
3.7
conductive dust
combustible dust with electrical resistivity equal to or less than 103 Ω•m
3.8
non-conductive dust
combustible dust with electrical resistivity greater than 103 Ω•m
3.9
combustible flyings
solid particles, including fibres, greater than 500 μm in nominal size, which may be suspended in air, may settle out of the atmosphere under their own weight, can burn or glow in air, and may form explosive mixtures with air at atmospheric pressure and normal temperatures
Note: Examples of fibres and flyings include rayon, cotton (including cotton linters and cotton waste), sisal, jute, hemp, cocoa fibre, oakum, and baled waste kapok.
Contents of GB/T 12476.3-2017
Foreword II
Introduction IV
1 Scope
2 Normative References
3 Terms and Definitions
4 Area Classification
5 Sources of Release
6 Zones
7 Dust Layer Hazard
8 Documentation
Annex A (Informative) Area Classification Application
Annex B (Informative) Risk of Fire from Hot Surface Ignition of Dust Layer
Annex C (Informative) Housekeeping
Annex D (Informative) Introduction of an Alternative Risk Assessment Method Encompassing ‘Equipment Protection Levels’ for Ex Equipment
Bibliography
