There are the following parts under the general title Explosive atmospheres:
——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 19: Fieldbus intrinsically safe concept (FISCO);
——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;
…
This is Part 12 of Explosive atmospheres.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces GB/T 12476.8-2010 Electrical apparatus for use in the presence of combustible dust - Part 8: Test methods - Methods for determining the minimum ignition temperatures of dust, GB/T 12476.9-2010 Electrical apparatus for use in the presence of combustible dust - Part 9: Test methods - Method for determining the electrical resistivity of dust in layers and GB/T 12476.10-2010 Electrical apparatus for use in the presence of combustible dust - Part 10: Test methods - Method for determining minimum ignition energy of dust/air mixtures. This part integrates the contents of GB/T 12476.8-2010, GB/T 12476.9-2010 and GB/T 12476.10-2010. The following main technical changes have been made with respect to GB/T 12476.8-2010, GB/T 12476.9-2010 and GB/T 12476.10-2010:
——Modified the requirements for dust samples (see Chapter 4, 4.1 and 5.1 of GB/T 12476.9-2010, Chapter 5 of GB/T 12476.9-2010, Chapter 5 of GB/T 12476.10-2010);
——Added the determination of combustible dust and combustible fly (see Chapter 5);
——Added the procedure to determine the characteristics of combustible dust or combustible fly (see Chapter 6);
——Modified the test method for the lowest ignition temperature of dust cloud (see 8.1, Chapter 5 of GB/T 12476.8-2010);
——Modified the test method for the lowest ignition temperature of the dust layer (see 8.2, Chapter 4 of GB/T 12476.8-2010);
——Method for determining the minimum ignition energy of dust/air mixture (see 8.3, Chapter 4 and Chapter 6 of GB/T 12476.10-2010);
——Modified the dust resistivity test (see 8.4, Chapter 4, Chapter 6 and Chapter 7 of GB/T 12476.9-2010);
——Added the measurement of the temperature distribution on the surface of the hot metal plate (see Appendix A);
——Added vertical pipe (improved Hartmann pipe) equipment (see Appendix D).
The translation method used in this part is equivalent to ISO/IEC 80079-20-2:2016 Explosive Atmosphere Part 20-2: Test Methods for Flammable Dust of Material Properties.
The following editorial changes have been made in this part:
——The standard name is changed;
——Include the contents of the errata ISO/IEC 80079-20-2:2016/COR1:2017;
——The network address of GESTIS-DUST-EX in Appendix G has been added for ease of use.
This part was proposed by the China Electrical Equipment Industrial Association.
This part is under the jurisdiction of SAC/TC 9 National Technical Committee on Explosion Protected Electrical Apparatus of Standardization Administration of China.
The previous editions of this part are as follows:
——GB/T 12476.8-2010;
——GB/T 12476.9-2010;
——GB/T 12476.10-2010.
Explosive atmospheres -
Part 12: Material characteristics for combustible dusts - Test methods
1 Scope
This part of Explosive Atmospheres describes the test methods for the identification of combustible dust and combustible dust layers in order to permit classification of areas where such materials exist for the purpose of the proper selection and installation of electrical and mechanical equipment for use in the presence of combustible dust.
The standard atmospheric conditions for determination of characteristics of combustible dusts are:
——Temperature: -20 °C to +60 °C；
——pressure 80 kPa to 110 kPa;
——air with normal oxygen content, typically 21% v/v.
The test methods defined do not apply to:
——recognized explosives, propellants (e.g. gunpowder, dynamite), or substances or mixtures of substances which may, under some circumstances, behave in a similar manner or
——dusts of explosives and propellants that do not require atmospheric oxygen for combustion, or to pyrophoric substances.
2 Normative references
None.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
combustible dust
finely divided solid particles, 500 µm or less in nominal size, which may form explosive mixtures with air at standard atmospheric pressure and 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 but does not preclude a hollow particle.
3.1.1
conductive dust
combustible metal dusts and other combustible dusts with electrical resistivity equal to or less than 1×103 Ω⋅m
Note 1: Metal dust is treated as conductive dust because it is assumed that surface oxidation cannot be depended upon to always ensure electrical resistivity greater than 1×103 Ω⋅m.
3.1.2
non-conductive dust
combustible dust with electrical resistivity greater than 1×103 Ω⋅m
3.2
combustible flyings
solid particles, including fibres, where one dimension is greater than 500 µm in nominal size, which may form an explosive mixture with air at standard atmospheric pressure and temperature
Note 1: The ratio of length to width is 3 or more.
Note 2: Examples of flyings include carbon fibre, rayon, cotton (including cotton linters and cotton waste), sisal, jute, hemp, cocoa fibre, oakum and baled waste kapok.
3.3
explosive dust atmosphere
mixture with air, under atmospheric conditions, of combustible substances in the form of dust, fibres, or flyings which, after ignition, permits self-sustaining propagation
3.4
minimum ignition temperature of a dust layer
lowest temperature of a hot surface at which ignition occurs in a dust layer under specified test conditions
3.5
minimum ignition temperature of a dust cloud
lowest temperature of a hot surface on which the most ignitable mixture of the dust with air is ignited under specified test conditions
3.6
minimum ignition energy (of a combustible dust/air mixture)
lowest electrical energy stored in a capacitor which upon discharge is sufficient to effect ignition of the most sensitive dust/air mixture under specified test conditions
4 Dust sample requirements
4.1 Receipt of sample for testing
A material safety data sheet or equivalent with the sample.
The test material should be provided in suitable packaging, labelled according to relevant guidelines labelled according to relevant guidelines, and appropriate transportation.
Note: It is usual to provide a quantity of at least 0.5 kg for testing. If sample preparation is required this may be insufficient. If only a smaller volume of material is available then the full range of testing may not be possible.
4.2 Characterisation of sample
The sample should be representative of the material as it appears in the entire process operated.
Note: Many unit operations such as extract systems will separate dust into finer fractions than seen in the main processing equipment and this is accounted for when taking the sample.
If the sample is not representative of the material as found in the process then sample preparation should be carried out to apply the worst case conditions.
At least the following information about the sample should be provided:
——minimum particle size,
——median particle size,
——particle distribution,
——moisture content,
——method of determination (e.g. optical methods or sieving).
If the applicant cannot provide usable data then this should be determined separately.
4.3 Preparation of sample
If it is not possible to test the sample as received, or if the sample is no longer representative of the process material then it may be necessary to condition or alter the sample for testing. This may include:
——grinding/sieving,
——drying and,
——humidifying.
Any apparent changes noted in the properties of the dust during preparation of the sample, for example, by sieving or owing to temperature or humidity conditions, should be stated in the test report.
Note 1: Sample preparation such as grinding and sieving, or drying can alter the material characteristics. Where finer fractions are present in a facility it is appropriate to take fractions of less than 63 µm to give the most easily ignitable mixtures. When the sample is a mixture of substances, the sample preparation can result in a change to the sample’s composition.
Note 2: The presence of solvents can become altered in the sample preparation process.
4.4 Test conditions
The tests should be carried out at standard atmospheric temperature of (20±10)°C and standard atmospheric pressure of 80 kPa to 110 kPa (0.8 bar to 1.1 bar) unless otherwise specified.
Foreword I
1 Scope
2 Normative references
3 Terms and definitions
4 Dust sample requirements
4.1 Receipt of sample for testing
4.2 Characterisation of sample
4.3 Preparation of sample
4.4 Test conditions
5 Combustible dusts and combustible flyings determination
5.1 Test sequence
5.2 Tests to determine whether material is a combustible dust or combustible flying
6 Procedure for characterisation of combustible dust or combustible flying
7 Test methods for determination of whether a material is a combustible dust or a combustible flying
7.1 Modified Hartmann tube
7.2 20-litre sphere
7.3 Alternative method to 20-litre sphere for small test material quantities
8 Test methods for combustible dust determinations
8.1 MIT of a dust cloud
8.2 Test for MIT of dust layer
8.3 Method for determining minimum ignition energy of dust/air mixtures
8.4 Test on resistivity
9 Test report
Annex A (Normative) Measurement of temperature distribution on the surface of the hot plate
Annex B (Informative) Godbert-Greenwald oven (GG)
Annex C (Informative) Examples of spark-generating systems
Annex D (Normative) Vertical tube (modified Hartmann tube) apparatus
Annex E (Informative) 20-litre sphere
Annex F (Informative) BAM oven
Annex G (Informative) Data for dust explosion characteristics
Annex H (Informative) 1 m3 vessel
Bibliography
