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This document is drafted in accordance with the rules given in the GB/T 1.1-2020 Directives for Standardization — Part 1: Rules for the Structure and Drafting of Standardizing Documents.
This part is Part 8 of GB/T 3836 Explosive Atmospheres. The following parts of GB/T 3836 have been published:
— Part 1: Equipment — General Requirements;
— Part 2: Equipment Protection by Flameproof Enclosures “d”;
— Part 3: Equipment Protection by Increased Safety “e”;
— Part 4: Equipment Protection by Intrinsic Safety "i";
— Part 5: Equipment Protection by Pressurized Enclosure “p”;
— Part 6: Equipment Protection by Oil Immersion “o”;
— Part 7: Equipment Protection by Powder Filling “q”;
— Part 8: Equipment Protection by Type of Protection “n”;
— Part 9: Equipment Protection by Type of Protection “m”;
— Part 11: Material Characteristics for Gas and Vapour Classification — Test Methods and Data;
— Part 12: Material Characteristics for Combustible Dusts — Test Methods;
— Part 13: Equipment Repair, Overhaul and Reclamation;
— Part 14: Classification of Areas — Explosive Gas Atmosphere;
— Part 15: Electrical Installations Design, Selection and Erection;
— Part 16: Electrical Installations Inspection and Maintenance;
— Part 17: Equipment Protection by Pressurized Room “p” and Artificially Ventilated Room “v”;
— Part 18: Intrinsically Safe Electrical Systems;
— Part 20: Equipment with Equipment Protection Level (EPL) Ga;
— Part 21: Application of Quality Systems for Equipment Manufacture;
— Part 22: Protection of Equipment and Transmission System using Optical Radiation;
— Part 23: Group I, Category EPL Ma Equipment Intended to Remain Functional in Atmospheres Endangered by Firedamp and/or Coal Dust
— Part 24: Equipment Protection by Special Protection “s”;
— Part 25: Requirements for Process Sealing between Flammable Process Fluids and Electrical Systems;
— Part 26: Electrostatic Hazards — Guidance;
— Part 27: Electrostatic Hazards — Test;
— Part 28: Non-electrical Equipment for Potentially Explosive Atmospheres — Basic Method and Requirements;
— Part 29: Non-electrical Equipment for Explosive Atmospheres — Constructional Safety “c”, Control of Ignition Source “b”, Liquid Immersion “k;
— Part 30: Equipment and Components in Explosive Atmospheres in Underground Mines;
— Part 31: Equipment Dust Ignition Protection by Enclosure “t”;
— Part 32: Intrinsically Safe Systems with Electronically Controlled Spark Duration Limitation;
— Part 33: Equipment in Adverse Service Conditions;
— Part 34: Equipment Assemblies;
— Part 35: Classification of Areas for Explosive Dust Atmospheres;
This document replaces 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 in whole, and the following technical deviations have been made with respect to the GB/T 12476.3-2017:
— dust cloud density and concentration are added as the factors for consideration of release (see 4.1);
— the requirement for competence of personnel is added (see 4.3);
— the requirement for “dust layers to be raised to form a dust cloud must be taken into consideration” is added (see Clause 7);
— EPL is added in documentation (see 8.1).
This document has been redrafted and modified adoption of International Standard IEC 60079-10-2:2015 Explosive Atmospheres — Part 10-2: Classification of Areas — Combustible Dust Atmospheres.
For the purposes of this document, the following structural adjustments have also been made:
— Annex A corresponds to Annex C of IEC 60079-10-2:2015, Annex B corresponds to Annex A of IEC 60079-10-2:2015, and Annex C corresponds to Annex B of IEC 60079-10-2:2015.
The technical deviations between this document and the International Standard IEC 60079-10-2:2015, together with their justifications, are given below:
— The adjustments on technical deviations have been made for the normative references of this document to adapt to the technical conditions in China, which are mainly reflected in Clause 2 "Normative References”, with the following specific content:
IEC 60079-0 is replaced by GB/T 3836.1 which is modified in relation to the international standard (see Clause 3);
IEC 60079-10-1 and ISO/IEC 80079-20-2 are deleted, and the corresponding documents GB 3836.14 and GB/T 3836.12 are moved to the Bibliography.
For the purposes of this document, the following editorial changes have also been made:
— In order to be consistent with the current standard series, the name of this document is modified to Explosive Atmospheres — Part 35: Classification of Areas for Explosive Dust Atmospheres;
— a paragraph on ISO and IEC terminology maintenance addresses is added in Clause 3;
— the incorrect reference of sub-clause number in Note 1 of 3.9 is deleted;
— the note on competence of personnel is delete from 4.3.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. The issuing body of this document shall not be held responsible for identifying any or all such patent rights.
This standard was proposed by China Electrical Equipment Industry Association.
This document is under the jurisdiction of National Technical Committee 9 on Explosion Protected Electrical Apparatus of Standardization Administration of China (SAC/TC 9).
The previous editions of this document and documents replaced by this document are as follows:
— The first edition was issued in 2007 as GB 12476.3-2007;
— The first edition was revised in 2017 as GB/T 12476.3-2017;
— This is the second revised edition, and the entire texts of GB/T 3836 were amalgamated.
Introduction
GB/T 3836 Explosive Atmospheres is prepared in order to establish the basic technical requirements for equipment used in explosive atmospheres and its application, covering the design, manufacture, inspection, selection, installation, inspection, maintenance, repair and site classification of equipment used in explosive atmospheres, and adopts the form of partial standards, including but not limited to the following parts:
— Part 1: Equipment — General Requirements;
— Part 2: Equipment Protection by Flameproof Enclosures “d”;
— Part 3: Equipment Protection by Increased Safety “e”;
— Part 4: Equipment Protection by Intrinsic Safety "i";
— Part 5: Equipment Protection by Pressurized Enclosure “p”;
— Part 6: Equipment Protection by Oil Immersion “o”;
— Part 7: Equipment Protection by Powder Filling “q”;
— Part 8: Equipment Protection by Type of Protection “n”;
— Part 9: Equipment Protection by Type of Protection “m”;
— Part 11: Material Characteristics for Gas and Vapour Classification — Test Methods and Data;
— Part 12: Material Characteristics for Combustible Dusts — Test Methods;
— Part 13: Equipment Repair, Overhaul and Reclamation;
— Part 14: Classification of Areas — Explosive Gas Atmosphere;
— Part 15: Electrical Installations Design, Selection and Erection;
— Part 16: Electrical Installations Inspection and Maintenance;
— Part 17: Equipment Protection by Pressurized Room “p” and Artificially Ventilated Room “v”;
— Part 18: Intrinsically Safe Electrical Systems;
— Part 20: Equipment with Equipment Protection Level (EPL) Ga;
— Part 21: Application of Quality Systems for Equipment Manufacture;
— Part 22: Protection of Equipment and Transmission System using Optical Radiation;
— Part 23: Group I, Category EPL Ma Equipment Intended to Remain Functional in Atmospheres Endangered by Firedamp and/or Coal Dust
— Part 24: Equipment Protection by Special Protection “s”;
— Part 25: Requirements for Process Sealing between Flammable Process Fluids and Electrical Systems;
— Part 26: Electrostatic Hazards — Guidance;
— Part 27: Electrostatic Hazards — Test;
— Part 28: Non-electrical Equipment for Potentially Explosive Atmospheres — Basic Method and Requirements;
— Part 29: Non-electrical Equipment for Explosive Atmospheres — Constructional Safety “c”, Control of Ignition Source “b”, Liquid Immersion “k;
— Part 30: Equipment and Components in Explosive Atmospheres in Underground Mines;
— Part 31: Equipment Dust Ignition Protection by Enclosure “t”;
— Part 32: Intrinsically Safe Systems with Electronically Controlled Spark Duration Limitation;
— Part 33: Equipment in Adverse Service Conditions;
— Part 34: Equipment Assemblies;
— Part 35: Classification of Areas for Explosive Dust Atmospheres;
The classification of areas for explosive dust atmospheres can provide guidance and basis for the selection and implementation of equipment and various explosion-proof measures. In terms of the standardization of this technology, GB 12476.3-2007 on the classification of areas for explosive dust atmospheres was prepared by modified adoption of IEC 61241-10 in 2007. Subsequently, it was revised as GB/T 12476.3-2017 on the base of IEC 60079-10-2 in 2017. Since the release and implementation of the standard, there has been a certain new development in the technology and methods of classification of areas for explosive dust atmospheres. In terms of international standards, the current edition of the corresponding standard is IEC 60079-10-2:2015, and its main technical contents may also be applied to China. At present, GB 12476 in China is also being revised and the entire texts of GB/T 3836 are amalgamated. In order to adapt to the development of technology and be consistent with the development of international standards, and coordinate with the revision of Chinese standard series, it is necessary to revise GB/T 12476.3 and amalgamate the entire texts of GB/T 3836.
Based on the main technical content of IEC 60079-10-2:2015, appropriate modifications have been made in this revision to adapt to the specific situation in China.
The following information is useful when using this document.
Dusts, as defined in this document, are hazardous because when they are dispersed in air by any means they may form potentially explosive atmospheres. Furthermore, layers of dust may ignite and act as ignition sources for an explosive atmosphere.
This document gives guidance on the identification and classification of areas where such hazards from dust can arise. It sets out the essential criteria against which the ignition hazards can be assessed and gives guidance on the design and control parameters which can be used in order to reduce such a hazard. General and special criteria, along with examples, are given for the process of identification and classification of hazardous areas.
Explosive Atmospheres — Part 35: Classification of Areas for Explosive Dust Atmospheres
1 Scope
This document 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 document, 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, ignition hazards for dust layers are described.
The examples in this document 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 document can also be followed when combustible fibres or flyings might cause a hazard.
This document 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 (see Note 1).
Note 1: Atmospheric conditions include variations in pressure and temperature above and below reference levels of 101.3 kPa and 20°C, provided that the variations have a negligible effect on the explosive properties of the combustible materials.
This document is not applicable to:
— underground mining areas;
— dusts of explosives that do not require atmospheric oxygen for combustion such as pyrophoric substances, propellants, pyrotechnics, munitions, peroxides, oxidizers, water-reactive elements or compounds, or other similar materials;
— catastrophic failures which are beyond the concept of abnormality dealt with in this document;
— any risk arising from an emission of toxic gas from the dust.
This document is not applicable to where a hazard might arise due to the presence of flammable gas or vapour, but the principles may be used in the assessment of a hybrid mixture (see also GB 3836.14).
Note 2: Additional guidance on hybrid mixtures is provided in Annex A.
This document does not take into account the effects of consequential damage following a fire or an explosion.
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/T 3836.1 Explosive Atmospheres — Part 1: Equipment — General Requirements (GB 3836.1-2021, IEC 60079-0:2017, MOD)
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB/T 3836.1 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC: http://www.electropedia.org/;
— ISO: http://www.iso.org/obp.
Note: Additional definitions applicable to explosive atmospheres can be found in GB/T 2900.35.
3.1
area
three-dimensional region or space
3.2
hybrid mixture
mixture of a flammable gas or vapour with a dust
3.3
dust
generic term including both combustible dust and combustible flyings
3.4
combustible dust
finely divided solid particles, 500 μm or less in nominal size, which may form an explosive mixture with air at atmospheric pressure and normal temperatures
Note 1: This includes dust and grit as defined in HJ 492.
Note 2: The term solid particles is intended to address particles in the solid phase and not the gaseous or liquid phase, but does not preclude a hollow particle.
Note 3: Materials passing a U.S. No. 40 Standard sieve as defined in ASTM E 11-04 are considered to meet the 500 μm criterion.
Note 4: Combustible dust test methods can be found in GB/T 3836.12.
3.5
explosive dust atmosphere
mixture with air, under atmospheric conditions, of flammable substances in the form of dust, which, after ignition, permits self-sustaining propagation
3.6
conductive dust
combustible dust with electrical resistivity equal to or less than 103Ω·m
Note: Conductive dust is classified as Group IIIC.
3.7
non-conductive dust
combustible dust with electrical resistivity greater than 103Ω·m
Note: Non-conductive dust is classified as Group IIIB.
3.8
combustible flyings
solid particles including fibers, greater than 500 μm in nominal size, which may form an explosive mixture with air at atmospheric pressure and normal temperatures
Note 1: Examples of flyings include rayon, cotton (including cotton linters and cotton waste) sisal, jute, hemp, cocoa fiber, okum and waste kapok.
Note 2: Combustible flyings are classified as Group IIIA.
3.9
hazardous area (dust)
area in which combustible dust, in the form of a cloud is present, or may be expected to be present, in quantities such as to require special precautions for the construction, installation and use of equipment
Note 1: Hazardous areas are divided into zones based upon the frequency and duration of the occurrence of explosive dust atmospheres (see 6.2).
Note 2: The potential of creating an explosive dust cloud from a dust layer also needs to be considered.
3.10
non-hazardous area (dust)
area in which combustible dust in the form of a cloud is not expected to be present in quantities such as to require special precautions for the construction, installation and use of equipment
3.11
dust containment
process equipment housing which is intended to handle, process, transport or store materials inside of it, while minimizing the risk of the release of dust to the surrounding atmosphere
3.12
source of dust release
point or location from which dust may be released into the atmosphere
Note: The source of dust release can be from a dust containment or from a dust layer.
3.13
continuous grade of release
release which is continuous or is expected to occur frequently or for long periods
3.14
continuous formation of a dust cloud
locations in which a dust cloud may exist continuously, or may be expected to continue for long periods or for short periods which occur frequently
3.15
primary grade of release
release which can be expected to occur periodically or occasionally during normal operation
3.16
secondary grade of release
release which is not expected to occur in normal operation and, if it does occur, is likely to do so only infrequently and for short periods
3.17
extent of zone
distance in any direction from the edge of a source of release to the point where the hazard associated with the release is considered to exist no longer
3.18
normal operation
operation of equipment conforming electrically and mechanically with its design specification and used within the limits specified by the manufacturer
Note: Minor releases of dust which may form a cloud or layer (e.g. releases from filters) can be part of normal operation.
3.19
abnormal operation
process-linked malfunctions that occur infrequently
3.20
catastrophic failure
occurrence which exceeds the design parameters of the process plant and control system resulting in major release of flammable material
Note: Catastrophic failure in this context is applied, for example, to the rupture of a storage silo or a pneumatic conveyor.
3.21
equipment (for explosive atmospheres)
general term including apparatus, fittings, devices, components, and the like used as a part of, or in connection with, an installation in an explosive atmosphere
3.22
ignition temperature of a dust layer
lowest temperature of a surface at which ignition occurs in a dust on the surface
Note: The ignition temperature of a dust layer may be determined by the test method given in GB/T 3836.12.
3.23
ignition temperature of a dust cloud
lowest temperature of the hot inner wall of a furnace at which ignition occurs in a dust cloud in air contained therein
Note: The ignition temperature of a dust cloud may be determined by the test method given in GB/T 3836.12.
3.24
verification dossier
set of documents showing the compliance of electrical equipment and installations
Note: Requirements for a ‘verification dossier’ are given in GB/T 3836.15.
3.25
zones
3.25.1
Zone 20
a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is present continuously, or for long periods or frequently
3.25.2
Zone 21
a place in which an explosive dust atmosphere, in the form of a cloud of dust in air, is likely to occur in normal operation occasionally
3.25.3
Zone 22
area in which an explosive dust atmosphere, in the form of a cloud of combustible dust in air, is not likely to occur in normal operation but, if it does occur, will persist for a short period only
Note: The potential of creating an explosive dust cloud from a dust layer also needs to be considered.
4 Area Classification
4.1 General
This document adopts the concept, similar to that used for flammable gases and vapour, of using area classification to give an assessment of the likelihood of an explosive dust atmosphere occurring.
Dusts form explosive atmospheres only at concentrations within the explosion range. Although a cloud with a very high concentration may not be explosive, the danger nevertheless exists that, should the concentration fall, it may enter the explosive range. Depending on the circumstances, not every source of release will necessarily produce an explosive dust atmosphere. Dust clouds are also rarely of uniform density and consideration should be given to possible variances in concentration within a cloud for any condition or release.
Dusts that are not removed by mechanical extraction or ventilation, settle out at a rate depending on properties, such as particle size, into layers or accumulations. It shall be taken into account that a dilute or small continuous source of release, in time, is able to produce a potentially hazardous dust layer.
The hazards presented by dusts are as follows:
— the formation of a dust cloud from any source of release, including a layer or accumulation, to form an explosive dust atmosphere (see Clause 5);
— the formation of dust layers, which are not likely to form a dust cloud, but may ignite due to self-heating or exposure to hot surfaces or thermal flux and cause a fire hazard or over- heating of equipment. The ignited layer may also act as an ignition source for an explosive atmosphere.
Since explosive dust clouds and dust layers may exist, any source of ignition should be avoided.
If the source of ignition cannot be avoided, then measures shall be taken to reduce the likelihood of dust and/or ignition sources so that the likelihood of coincidence is so small as to make the risk negligible.
Note: In some cases, where the risk of explosion cannot be completely avoided, it can be necessary to employ some form of explosion protection such as explosion venting, explosion suppression or explosion isolation.
Subsequent to the completion of the area classification, a risk assessment may be carried out to assess whether the consequences of ignition of an explosive atmosphere requires the use of equipment of a higher equipment protection level (EPL) or may justify the use of equipment with a lower equipment protection level than normally required.
In this document, explosive dust atmospheres and dust layers are treated separately. In this clause, area classification for explosive dust clouds is described, with dust layers acting as one of the possible sources of release. Considerations for dust layers are described in Clause 7.
Foreword II
Introduction VI
1 Scope
2 Normative References
3 Terms and Definitions
4 Area Classification
4.1 General
4.2 Area classification procedure for explosive dust atmospheres
4.3 Competence of personnel
5 Sources of Release
5.1 General
5.2 Dust containment
5.3 Identification and grading of sources of release
6 Zones
6.1 General
6.2 Extent of zones
7 Dust Layers
8 Documentation
8.1 General
8.2 Drawings, data sheets and tables
Annex A (Informative) Hybrid Mixtures
Annex B (Informative) Area Classification Examples
Annex C (Informative) Housekeeping
Bibliography
