Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
GB/T 3836, under the general title of “Explosive Atmospheres”, is composed of:
—— 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 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: Construction and Use of Rooms or Buildings Protected by Pressurization;
—— 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.
……
This is Part 15 of “Explosive Atmospheres”.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces “Electrical Apparatus for Explosive Gas Atmospheres - Part 15: Electrical Installations in Hazardous Areas (other than Mines)” (GB 3836.15-2000) and “Electrical Apparatus for Use in the Presence of combustible dust - Part 2: Selection and Installation” (GB 12476.2-2010). The following main changes have been made in this revision with respect to GB 3836.15-2000 and GB 12476.2-2010:
—— some terms are added: competent body (see 3.1.1), zones (see 3.2.5), zone 0 (see 3.2.6), zone 1 (see 3.2.7), zone 2 (see 3.2.8), flameproof enclosure (see 3.3), increased safety (see 3.4), intrinsic safety “i” (see 3.5.1), galvanic isolation (see 3.5.3), intrinsically safe circuit (see 3.5.5), intrinsically safe electrical system (see 3.5.6), intrinsically safe sub-circuit (see 3.5.7), pressurization (see 3.7), type of protection “n” (see 3.8), oil-immersion “o” (see 3.9), powder filling “q” (see 3.10), encapsulation “m” (see 3.11), electrical supply systems (see 3.13), equipment (see 3.14);
—— in the name of the standard, “Explosive Gas Atmospheres” is changed into “Explosive Atmospheres”, and the explosive gas atmosphere and explosive dust atmosphere are combined as one;
—— equipment protection levels (EPLs) is introduced (see Annex I);
—— knowledge, skills and competencies of responsible persons, operatives and designers are explained in Annex F;
—— the requirements for selection and installation of ultrasonic radiation equipment, optical radiation are added (see 5.7, 5.8 and 6.8);
—— preventive requirement for explosion in dust hazardous areas is deleted (4.9 of GB 12476.2-2010).
This part is redrafted and modified in relation to “Explosive Atmospheres - Part 14: Electrical Installations Design, Selection and Erection” (IEC 60079-14:2007).
The structural adjustments have been made with respect to IEC 60079-14: 2007:
—— 5.6.3.1 General, 5.7.1 General, 5.8.1 General, 5.8.3.1 General, 5.10.1 General, 5.14.1 General, 6.2.1 General, 6.3.2.1 General, 9.3.1 General, 11.1 General, and 13.1 General are added, and clause numbers are extended accordingly;
—— 1) and 2) of 13.3.5 are modified to 13.4.5.1 and 13.4.5.2;
—— the “pressurized room and analysis room” in the title of 13.4.1 is deleted, and the clause number of 13.4.1.1 is modified to 13.5.1, and 134.1.2 to 13.5.2;
—— the clause of “B.1 Intrinsically safe circuit” in Annex B is deleted.
The following main technical differences have been made with respect to IEC 60079-14: 2007:
—— the adjustment in "Normative References" of this part has technical differences to meet the technical specification in China; the adjustment situations are embodied in a concentrated way in Clause 2 - "Normative References" and the specific adjustments are as follows:
IEC 60950 is replaced with GB 4943.1 which is modified in relation to the international standard;
IEC 60079-7, IEC 60079-6, IEC 60079-5, IEC 60079-18, IEC 60079-10, IEC 60079-17, IEC/TR 60079-13, IEC 60079-27, IEC 60079-26 are respectively replaced by GB 3836.3-2010, GB 3836.6, GB 3836.7, GB 3836.9-2014, GB 3836.14-2014, GB/T 3836.16-2017, GB 3836.17-2007, GB 3836.19-2010, GB 3836.20-2010 which are identical to the foregoning international standards; IEC 60079-0, IEC 60079-1, IEC 60079-11, IEC 60079-2, IEC 60079-15, IEC 60079-19, IEC 60079-25, IEC 60079-28 are respectively replaced by GB 3836.1-2010, GB 3836.2-2010, GB 3836.4-2010, GB/T 3836.5-2017, GB 3836.8-2014, GB 3836.13-2013, GB/T 3836.18-2017, GB/T 3836.22-2017 which are modified in relation to the foregoing international standards;
IEC 60079-10-2, IEC 61241-11, IEC 61241-1, IEC 61241-18, IEC 61241-4, IEC 61241-2-1 are respectively replaced by GB/T 12476.3-2017, GB 12476.4-2010, GB 12476.5-2013, GB 12476.6-2010, GB 12476.7-2010, GB 12476.8-2010, which are identical to the foregoing international standards; IEC 61241-0 is replaced by GB 12476.1-2013 which is modified in relation to the foregoing international standard;
IEC 60364-4-41 is replaced by GB/T 16895.21-2011, which is identical to the foregoing international standard;
IEC 62305-3 is replaced by GB/T 21714.3-2015, which is identical to the foregoing international standard;
the references IEC 60050-826 and IEC 60364 (all parts) are deleted;
—— the specification for “equipment without explosion-proof certificate” in 4.3.2 is modified as “apart from simple apparatus used within an intrinsically safe circuit in accordance with the provisions of GB 3836.4-2010 and GB/T 3836.18-2017, the equipment without certificate shall be restricted in explosion hazards” ;
—— see the note in Table 3 for application restriction of increased safety “e” in hazardous area zone 1;
—— considering the current coexistence of national standards GB 3836 series (equipment for explosive gas atmospheres) and GB 12476 series (electrical apparatus for use in the presence of combustible dust), equipment for use in the presence of combustible dust stipulated in GB 12476 series standards can still be used in zones 20, 21 and 22;
—— Table 2 “Selection of Type of Protection in Dust Hazards” (see 5.3) is added, and the numbers of tables are extended accordingly.
The following editorial changes are made in this part:
—— the standard name is modified;
—— non-normative references ISO 10807, IEC 60079 (all parts), IEC 61241 (all parts), IEC 60079-29-1 and IEC 60079-29-2 are deleted.
This part was proposed by 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.
Drafting organizations of this part: Nanyang Explosion Protected Electrical Apparatus Research Institute, China National Quality Supervision and Test Centre for Explosion Protected Electrical Products, SINOPEC Engineering Incorporation, Warom Technology Incorporated Company, CZ Explosion-proof Electric Appliances Co., Ltd., CNOOC Safety & Technology Services Co., Ltd., Shanghai Baolin Explosion-proof Electric Co., Ltd. and Sunleem Technology Incorporated Company.
Chief drafters of this part: Wang Jun, Zhang Gang, Wang Zongjing, Li Shuzhao, Wang Yade, Weng Zhenke, Zheng Zhenxiao, Liu Kai, Zhang Yuda.
The previous editions of this part are as follows:
—— GB 3836.15-2000;
—— GB 12476.2-2006, GB 12476.2-2010.
Introduction
Preventive measures to reduce the explosion risk from flammable materials are based on three principles, which shall be applied in the following order:
1) substitution;
2) control;
3) mitigation.
Substitution involves, for example, replacing a flammable material by one which is either not flammable or less flammable.
Control involves, for example:
a) reducing the quantity of flammables;
b) avoiding or minimising releases;
c) controlling the release;
d) preventing the formation of an explosive atmosphere;
e) collecting and containing releases; and
f) avoiding ignition sources.
Note 1 With the exception of item f), all of the above are part of the process of hazardous area classification.
Mitigation involves, for example:
1) reducing the number of people exposed;
2) providing measures to avoid the propagation of an explosion;
3) providing explosion pressure relief;
4) providing explosion pressure suppression; and
5) providing suitable personal protective equipment.
Note 2: The above items are part of consequence management if considering risk.
Once the principles of substitution and control (items a) to e)) have been applied, the remaining hazardous areas should be classified into zones according to the likelihood of an explosive atmosphere being present (see GB 3836.14-2014 or GB/T 12476.3-2017). Such classification, which may be used in conjunction with an assessment of the consequences of an ignition, allows equipment protection levels to be determined and hence appropriate types of protection to be specified for each location.
For an explosion to occur, an explosive atmosphere and a source of ignition need to co-exist. Protective measures aim to reduce, to an acceptable level, the likelihood that the electrical installation could become a source of ignition.
By careful design of the electrical installation, it is frequently possible to locate much of the electrical equipment in less hazardous or non-hazardous areas.
If electrical equipment is to be installed in areas where dangerous concentrations and quantities of flammable gases, vapours, mists or dusts may be present in the atmosphere, protective measures are applied to reduce the likelihood of explosion due to ignition by arcs, sparks or hot surfaces, produced either in normal operation or under specified fault conditions.
Many types of dust that are generated, processed, handled and stored, are combustible. If ignited they can burn rapidly and with considerable explosive force if mixed with air in the appropriate proportions. It is often necessary to use electrical apparatus in locations where such combustible materials are present, and suitable precautions must therefore be taken to ensure that all such apparatus is adequately protected so as to reduce the likelihood of ignition of the external explosive atmosphere. In electrical apparatus, potential ignition sources include electrical arcs and sparks, hot surfaces and frictional sparks.
Areas where dust, flyings and fibres in air occur in dangerous quantities are classified as hazardous and are divided into three zones according to the level of risk.
Combustible dust can be ignited by equipment in several ways:
By surfaces of the apparatus that are above the minimum ignition temperature of the dust concerned. The temperature at which a type of dust ignites is a function of the properties of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the geometry of the heat source.
By arcing or sparking of electrical parts such as switches, contacts, commutators, brushes, or the like.
By discharge of an accumulated electrostatic charge.
By radiated energy (e.g. electromagnetic radiation).
By mechanical sparking or frictional sparking associated with the apparatus.
In order to avoid dust ignition hazards it is necessary that:
The temperature of surfaces on which dust can be deposited, or which would be in contact with a dust cloud, is kept below the temperature limitation specified in this standard.
Any electrical sparking parts, or parts having a temperature above the temperature limit specified in this standard:
—— are contained in an enclosure which adequately prevents the ingress of dust, or
—— the energy of electrical circuits is limited so as to avoid arcs, sparks or temperatures capable of igniting combustible dust.
Any other ignition sources are avoided.
Several types of protection are available for electrical equipment in hazardous areas (see GB 3836.1-2010), and this part gives the specific requirements for design, selection and erection of electrical installations in explosive atmospheres.
This part is supplementary to other relevant national standards, for example series standard of electrical installations for buildings (requirements for electrical installation). This part also refers to GB 3836.1-2010 and its associated standards for the construction, testing and marking requirements of suitable electrical equipment.
This part is based on the assumption that electrical equipment is correctly installed, tested, maintained and used in accordance with its specified characteristics.
Inspection, maintenance and repair aspects play an important role in control of hazardous area installations and the user’s attention is drawn to GB 3836.13-2013 and GB/T 3836.16-2017 for further information concerning these aspects.
In any industrial installation, irrespective of size, there may be numerous sources of ignition apart from those associated with electrical equipment. Precautions may be necessary to ensure safety from other possible ignition sources, but guidance on this aspect is outside the scope of this part. See GB 25285.1 and GB 25285.2 for relevant content.
In GB 12476.5-2013, for protection by enclosure “tD”, two different types of practice, A and B, are specified and are intended to provide an equivalent level of protection.
Both of these practices are in common use and the requirements of each should be followed without mixing either the apparatus requirements or selection/installation requirements of the two practices. They adopt different methodology with the primary differences being:
Practice A Practice B
Written principally as performance based requirements Written as both performance and prescriptive based requirements
Maximum surface temperature is determined with 5 mm layer of dust and installation rules require 75 °C margin between the surface temperature and ignition temperature of the particular dust Maximum surface temperature is determined with 12.5 mm layer of dust and installation rules require 25℃ margin between the surface temperature and ignition temperature of the particular dust
A method of achieving the required dust ingress protection by the use of resilient seals on joints and rubbing seals on rotating or moving shafts or spindles. Determine dust ingress protection grade according to the enclosure protection grade (IP Code) of GB/T 4208. A method of achieving the required dust ingress protection by specified widths and clearances between joint faces and, in the case of shafts and spindles, specified lengths and diametrical clearances between moving and stationary parts. Determine dust ingress protection grade according to the heat cycling test
Explosive atmosphere - Part 15: Electrical Installations Design, Selection and Erection
爆炸性环境
第15部分：电气装置的设计、选型和安装
1 Scope
This part of “Explosive Atmosphere” contains the specific requirements for the design, selection and erection of electrical installations in hazardous areas associated with explosive atmospheres.
Where the equipment is required to meet other environmental conditions, for example, protection against ingress of water and resistance to corrosion, additional methods of protection may be necessary. The method used shall not adversely affect the integrity of the enclosure.
The requirements of this standard apply only to the use of equipment under normal or near normal atmospheric conditions. For other conditions, additional precautions may be necessary. For example, most flammable materials and many materials which are normally regarded as non-flammable might burn vigorously under conditions of oxygen enrichment. Other precautions might also be necessary in the use of equipment under conditions of extreme temperature and pressure. Such precautions are beyond the scope of this part.
These requirements are in addition to the requirements for installations in non-hazardous areas.
This part applies to all electrical equipment including fixed, portable, transportable and personal, and installations, permanent or temporary.
It applies to installations at all voltages.
This part does not apply to:
—— electrical installations in mines susceptible to firedamp;
Note: This part may apply to electrical installations in mines where explosive gas atmospheres other than firedamp may be formed and to electrical installations in the surface installation of mines.
—— inherently explosive situations and dust from explosives or pyrophoric substances (for example explosives manufacturing and processing);
—— rooms used for medical purposes;
—— electrical installations in areas where the hazard is due to hybrid mixtures of combustible dust and explosive gas, vapour or mist.
This part does not take into account of any risk due to an emission of flammable or toxic gas from the dust.
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 3836.20-2010 Explosive Atmospheres - Part 20: Equipment with Equipment Protection Level (EPL) Ga (IEC 60079-26: 2006, IDT)
GB/T 3836.22-2017 Explosive Atmospheres - Part 22: Protection of Equipment and Transmission System using Optical Radiation (IEC 60079-28: 2006, MOD)
GB/T 4208 Degrees of Protection Provided by Enclosure (IP Code) (GB/T 4208-2017, IEC 60529: 2013, IDT)
GB 4793.1 Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use-Part 1: General Requirements (GB 4793.1-2007, IEC 61010-1:2001, IDT)
GB/T 4942.1 Degrees of Protection Provided by the Integral Design of Rotating Electrical Machined (IP Code) - Classification (GB/T 4942.1-2006, IEC 60034-5: 2000, IDT)
GB 4943.1 Information Technology Equipment - Safety - Part 1: General Requirements (GB 4943.1-2011, IEC 60950-1: 2005, MOD)
GB 12476.1-2013 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 1: General Requirements (IEC 61241-0: 2004, MOD)
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 (IEC 60079-10-2: 2009, IDT)
GB 12476.4-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 4: Protection by Intrinsic Safety “iD” (IEC 61241-11: 2005, IDT)
GB 12476.5-2013 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 5: Protection by Enclosures “tD” (IEC 61241-1: 2004, IDT)
GB 12476.6-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 6: Protection by Enclosures “tD” (IEC 61241-18: 2004, IDT)
GB 12476.7-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 7: Type of Protection “pD” (IEC 61241-4: 2001, IDT)
GB 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 (IEC 61241-2-1: 1994, IDT)
GB/T 16895.21-2011 Low-voltage Electrical Installations - Part 4-41: Protection for Safety - Protection Against Electric Shock (IEC 60364-4-41: 2005, IDT)
GB/T 16927.1 High-voltage Test Techniques - Part 1: General Definitions and Test Requirements (GB/T 16927.1-2011, IEC 60060-1:2006, MOD)
GB/T 18380.12 Test on Electric and Optical Fibre Cables under Fire Conditions - Part 12 Test for Vertical Flame Propagation for a Single Insulated Wire or Cable - Procedure for 1kW Pre-mixed Flame (GB/T 18380.12-2008, IEC 60332-1-2: 2004, IDT)
GB/T 19212.7 Safety of Transformers, Reactors, Power Supply Units and Similar Products for Supply Voltages up to 1 100 V - Part 7: Particular Requirements and Test for Safety Isolating Transformers and Power Supply Units Incorporating Saftey Isolating Transformers (GB/T 19212.7-2012, IEC 61558-2-6: 2009,IDT)
GB/T 21714.3-2015 Protection Against Lightning - Part 3: Physical Damage to Structures and Life Hazard (IEC 62305-3: 2010, IDT)
GB/T 29812 Industrial-process Control - Safety of Analyser Houses.
IEC 60079-16 Electrical Apparatus for Explosive Gas Atmospheres - Part 16:Artificial Ventilation for the Protection of Analyzer(s) Houses
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB 3836.1-2010 and the following apply.
Note: Additional definitions applicable to explosive atmospheres can be found in GB/T 2900.35-2008.
3.1 general
3.1.1
competent body
individual or organization which can demonstrate appropriate technical knowledge and relevant skills to make the necessary assessments of the safety aspect under consideration
3.1.2
verification dossier
set of documents showing the compliance of electrical equipment and installations
3.2 hazardous areas
3.2.1
hazardous areas
area in which an explosive atmosphere 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: For the purposes of this art, an area is a three-dimensional region or space.
3.2.2
non-hazardous area
area in which an explosive atmosphere is not expected to be present in quantities such as to require special precautions for the construction, installation and use of equipment
3.2.3
group (of an electrical equipment for explosive atmospheres)
classification of electrical equipment related to the explosive atmosphere for which it is to be used
Note: Electrical equipment for use in explosive atmospheres is divided into three groups:
—— group I: electrical equipment for mines susceptible to firedamp;
—— group II (which can be divided into subgroups): electrical equipment for places with an explosive gas atmosphere, other than mines susceptible to firedamp (methane) (see 5.5);
—— group III (which can be divided into subgroups): electrical equipment for places with an explosive dust atmosphere (see 5.5).
3.2.4
maximum permissible surface temperature
highest temperature that a surface of electrical apparatus is allowed to reach in practical service to avoid ignition
Note: The maximum permissible surface temperature will depend upon the type of dust, whether as a cloud or layer, if a layer, its thickness and the application of a safety factor. For details see 5.6.3.
3.2.5
Zones
hazardous areas classified into zones based upon the frequency of the occurrence and duration of an explosive atmosphere
3.2.6
zone 0
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently
3.2.7
zone 1
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally
3.2.8
zone 2
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only
Foreword I Introduction V 1 Scope 2 Normative References 3 Terms and Definitions 4 General 5 Selection of Equipment (Excluding Cables and Conduits) 6 Protection from Dangerous (Incendive) Sparking 7 Electrical Protection 8 Emergency Switch-off and Electrical Isolation 9 Wiring Systems 10 Additional Requirements for Type of Protection "d" - Flameproof Enclosures 11 Additional Requirements for Type of Protection "e" - Increased Safety 12 Additional Requirements for Type of Protection "i" - Intrinsic Safety 13 Additional Requirements for Type of Protection 'p" - Pressurized Enclosures 14 Additional Requirements for Type of Protection 'n' 15 Additional Requirements for Type of Protection 'o’ - Oil Immersion 16 Additional Requirements for Type of Protection 'q' - Powder Filling 17 Additional Requirements for Type of Protection 'm’ - Encapsulation 18 Additional Requirements for Type of Protection 'tD' – Protection by Enclosure Annex A (Normative) Verification of Intrinsically Safe Circuits with More than One Associated Apparatus with Linear Current/Voltage Characteristics Annex B (Informative) Methods of Determining the Maximum System Voltages and Currents in Intrinsically Safe Circuits with More than One Associated Apparatus with Linear Current/Voltage Characteristics (as Required by Annex A) Annex C (Informative) Determination of Cable Parameters Annex D (Informative) Safe Work Procedure Guidelines for Explosive Gas Atmospheres Annex E (Normative) Potential Stator Winding Discharge Risk Assessment - Ignition Risk Factors Annex F (Normative) Knowledge, Skills and Competencies of Responsible Persons, Operatives and Designers Annex G (Informative) Examples of Dust Layers of Excessive Thickness Annex H (Normative) Frictional Sparking Risks with Light Metals and Their Alloys Annex I (Informative) Introduction of an Alternative Risk Assessment Method Encompassing “Equipment Protection Levels” for Ex Equipment Bibliography
Codeofchina.com is in charge of this English translation. In case of any doubt about the English translation, the Chinese original shall be considered authoritative.
GB/T 3836, under the general title of “Explosive Atmospheres”, is composed of:
—— 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 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: Construction and Use of Rooms or Buildings Protected by Pressurization;
—— 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.
……
This is Part 15 of “Explosive Atmospheres”.
This part is developed in accordance with the rules given in GB/T 1.1-2009.
This part replaces “Electrical Apparatus for Explosive Gas Atmospheres - Part 15: Electrical Installations in Hazardous Areas (other than Mines)” (GB 3836.15-2000) and “Electrical Apparatus for Use in the Presence of combustible dust - Part 2: Selection and Installation” (GB 12476.2-2010). The following main changes have been made in this revision with respect to GB 3836.15-2000 and GB 12476.2-2010:
—— some terms are added: competent body (see 3.1.1), zones (see 3.2.5), zone 0 (see 3.2.6), zone 1 (see 3.2.7), zone 2 (see 3.2.8), flameproof enclosure (see 3.3), increased safety (see 3.4), intrinsic safety “i” (see 3.5.1), galvanic isolation (see 3.5.3), intrinsically safe circuit (see 3.5.5), intrinsically safe electrical system (see 3.5.6), intrinsically safe sub-circuit (see 3.5.7), pressurization (see 3.7), type of protection “n” (see 3.8), oil-immersion “o” (see 3.9), powder filling “q” (see 3.10), encapsulation “m” (see 3.11), electrical supply systems (see 3.13), equipment (see 3.14);
—— in the name of the standard, “Explosive Gas Atmospheres” is changed into “Explosive Atmospheres”, and the explosive gas atmosphere and explosive dust atmosphere are combined as one;
—— equipment protection levels (EPLs) is introduced (see Annex I);
—— knowledge, skills and competencies of responsible persons, operatives and designers are explained in Annex F;
—— the requirements for selection and installation of ultrasonic radiation equipment, optical radiation are added (see 5.7, 5.8 and 6.8);
—— preventive requirement for explosion in dust hazardous areas is deleted (4.9 of GB 12476.2-2010).
This part is redrafted and modified in relation to “Explosive Atmospheres - Part 14: Electrical Installations Design, Selection and Erection” (IEC 60079-14:2007).
The structural adjustments have been made with respect to IEC 60079-14: 2007:
—— 5.6.3.1 General, 5.7.1 General, 5.8.1 General, 5.8.3.1 General, 5.10.1 General, 5.14.1 General, 6.2.1 General, 6.3.2.1 General, 9.3.1 General, 11.1 General, and 13.1 General are added, and clause numbers are extended accordingly;
—— 1) and 2) of 13.3.5 are modified to 13.4.5.1 and 13.4.5.2;
—— the “pressurized room and analysis room” in the title of 13.4.1 is deleted, and the clause number of 13.4.1.1 is modified to 13.5.1, and 134.1.2 to 13.5.2;
—— the clause of “B.1 Intrinsically safe circuit” in Annex B is deleted.
The following main technical differences have been made with respect to IEC 60079-14: 2007:
—— the adjustment in "Normative References" of this part has technical differences to meet the technical specification in China; the adjustment situations are embodied in a concentrated way in Clause 2 - "Normative References" and the specific adjustments are as follows:
IEC 60950 is replaced with GB 4943.1 which is modified in relation to the international standard;
IEC 60079-7, IEC 60079-6, IEC 60079-5, IEC 60079-18, IEC 60079-10, IEC 60079-17, IEC/TR 60079-13, IEC 60079-27, IEC 60079-26 are respectively replaced by GB 3836.3-2010, GB 3836.6, GB 3836.7, GB 3836.9-2014, GB 3836.14-2014, GB/T 3836.16-2017, GB 3836.17-2007, GB 3836.19-2010, GB 3836.20-2010 which are identical to the foregoning international standards; IEC 60079-0, IEC 60079-1, IEC 60079-11, IEC 60079-2, IEC 60079-15, IEC 60079-19, IEC 60079-25, IEC 60079-28 are respectively replaced by GB 3836.1-2010, GB 3836.2-2010, GB 3836.4-2010, GB/T 3836.5-2017, GB 3836.8-2014, GB 3836.13-2013, GB/T 3836.18-2017, GB/T 3836.22-2017 which are modified in relation to the foregoing international standards;
IEC 60079-10-2, IEC 61241-11, IEC 61241-1, IEC 61241-18, IEC 61241-4, IEC 61241-2-1 are respectively replaced by GB/T 12476.3-2017, GB 12476.4-2010, GB 12476.5-2013, GB 12476.6-2010, GB 12476.7-2010, GB 12476.8-2010, which are identical to the foregoing international standards; IEC 61241-0 is replaced by GB 12476.1-2013 which is modified in relation to the foregoing international standard;
IEC 60364-4-41 is replaced by GB/T 16895.21-2011, which is identical to the foregoing international standard;
IEC 62305-3 is replaced by GB/T 21714.3-2015, which is identical to the foregoing international standard;
the references IEC 60050-826 and IEC 60364 (all parts) are deleted;
—— the specification for “equipment without explosion-proof certificate” in 4.3.2 is modified as “apart from simple apparatus used within an intrinsically safe circuit in accordance with the provisions of GB 3836.4-2010 and GB/T 3836.18-2017, the equipment without certificate shall be restricted in explosion hazards” ;
—— see the note in Table 3 for application restriction of increased safety “e” in hazardous area zone 1;
—— considering the current coexistence of national standards GB 3836 series (equipment for explosive gas atmospheres) and GB 12476 series (electrical apparatus for use in the presence of combustible dust), equipment for use in the presence of combustible dust stipulated in GB 12476 series standards can still be used in zones 20, 21 and 22;
—— Table 2 “Selection of Type of Protection in Dust Hazards” (see 5.3) is added, and the numbers of tables are extended accordingly.
The following editorial changes are made in this part:
—— the standard name is modified;
—— non-normative references ISO 10807, IEC 60079 (all parts), IEC 61241 (all parts), IEC 60079-29-1 and IEC 60079-29-2 are deleted.
This part was proposed by 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.
Drafting organizations of this part: Nanyang Explosion Protected Electrical Apparatus Research Institute, China National Quality Supervision and Test Centre for Explosion Protected Electrical Products, SINOPEC Engineering Incorporation, Warom Technology Incorporated Company, CZ Explosion-proof Electric Appliances Co., Ltd., CNOOC Safety & Technology Services Co., Ltd., Shanghai Baolin Explosion-proof Electric Co., Ltd. and Sunleem Technology Incorporated Company.
Chief drafters of this part: Wang Jun, Zhang Gang, Wang Zongjing, Li Shuzhao, Wang Yade, Weng Zhenke, Zheng Zhenxiao, Liu Kai, Zhang Yuda.
The previous editions of this part are as follows:
—— GB 3836.15-2000;
—— GB 12476.2-2006, GB 12476.2-2010.
Introduction
Preventive measures to reduce the explosion risk from flammable materials are based on three principles, which shall be applied in the following order:
1) substitution;
2) control;
3) mitigation.
Substitution involves, for example, replacing a flammable material by one which is either not flammable or less flammable.
Control involves, for example:
a) reducing the quantity of flammables;
b) avoiding or minimising releases;
c) controlling the release;
d) preventing the formation of an explosive atmosphere;
e) collecting and containing releases; and
f) avoiding ignition sources.
Note 1 With the exception of item f), all of the above are part of the process of hazardous area classification.
Mitigation involves, for example:
1) reducing the number of people exposed;
2) providing measures to avoid the propagation of an explosion;
3) providing explosion pressure relief;
4) providing explosion pressure suppression; and
5) providing suitable personal protective equipment.
Note 2: The above items are part of consequence management if considering risk.
Once the principles of substitution and control (items a) to e)) have been applied, the remaining hazardous areas should be classified into zones according to the likelihood of an explosive atmosphere being present (see GB 3836.14-2014 or GB/T 12476.3-2017). Such classification, which may be used in conjunction with an assessment of the consequences of an ignition, allows equipment protection levels to be determined and hence appropriate types of protection to be specified for each location.
For an explosion to occur, an explosive atmosphere and a source of ignition need to co-exist. Protective measures aim to reduce, to an acceptable level, the likelihood that the electrical installation could become a source of ignition.
By careful design of the electrical installation, it is frequently possible to locate much of the electrical equipment in less hazardous or non-hazardous areas.
If electrical equipment is to be installed in areas where dangerous concentrations and quantities of flammable gases, vapours, mists or dusts may be present in the atmosphere, protective measures are applied to reduce the likelihood of explosion due to ignition by arcs, sparks or hot surfaces, produced either in normal operation or under specified fault conditions.
Many types of dust that are generated, processed, handled and stored, are combustible. If ignited they can burn rapidly and with considerable explosive force if mixed with air in the appropriate proportions. It is often necessary to use electrical apparatus in locations where such combustible materials are present, and suitable precautions must therefore be taken to ensure that all such apparatus is adequately protected so as to reduce the likelihood of ignition of the external explosive atmosphere. In electrical apparatus, potential ignition sources include electrical arcs and sparks, hot surfaces and frictional sparks.
Areas where dust, flyings and fibres in air occur in dangerous quantities are classified as hazardous and are divided into three zones according to the level of risk.
Combustible dust can be ignited by equipment in several ways:
By surfaces of the apparatus that are above the minimum ignition temperature of the dust concerned. The temperature at which a type of dust ignites is a function of the properties of the dust, whether the dust is in a cloud or layer, the thickness of the layer and the geometry of the heat source.
By arcing or sparking of electrical parts such as switches, contacts, commutators, brushes, or the like.
By discharge of an accumulated electrostatic charge.
By radiated energy (e.g. electromagnetic radiation).
By mechanical sparking or frictional sparking associated with the apparatus.
In order to avoid dust ignition hazards it is necessary that:
The temperature of surfaces on which dust can be deposited, or which would be in contact with a dust cloud, is kept below the temperature limitation specified in this standard.
Any electrical sparking parts, or parts having a temperature above the temperature limit specified in this standard:
—— are contained in an enclosure which adequately prevents the ingress of dust, or
—— the energy of electrical circuits is limited so as to avoid arcs, sparks or temperatures capable of igniting combustible dust.
Any other ignition sources are avoided.
Several types of protection are available for electrical equipment in hazardous areas (see GB 3836.1-2010), and this part gives the specific requirements for design, selection and erection of electrical installations in explosive atmospheres.
This part is supplementary to other relevant national standards, for example series standard of electrical installations for buildings (requirements for electrical installation). This part also refers to GB 3836.1-2010 and its associated standards for the construction, testing and marking requirements of suitable electrical equipment.
This part is based on the assumption that electrical equipment is correctly installed, tested, maintained and used in accordance with its specified characteristics.
Inspection, maintenance and repair aspects play an important role in control of hazardous area installations and the user’s attention is drawn to GB 3836.13-2013 and GB/T 3836.16-2017 for further information concerning these aspects.
In any industrial installation, irrespective of size, there may be numerous sources of ignition apart from those associated with electrical equipment. Precautions may be necessary to ensure safety from other possible ignition sources, but guidance on this aspect is outside the scope of this part. See GB 25285.1 and GB 25285.2 for relevant content.
In GB 12476.5-2013, for protection by enclosure “tD”, two different types of practice, A and B, are specified and are intended to provide an equivalent level of protection.
Both of these practices are in common use and the requirements of each should be followed without mixing either the apparatus requirements or selection/installation requirements of the two practices. They adopt different methodology with the primary differences being:
Practice A Practice B
Written principally as performance based requirements Written as both performance and prescriptive based requirements
Maximum surface temperature is determined with 5 mm layer of dust and installation rules require 75 °C margin between the surface temperature and ignition temperature of the particular dust Maximum surface temperature is determined with 12.5 mm layer of dust and installation rules require 25℃ margin between the surface temperature and ignition temperature of the particular dust
A method of achieving the required dust ingress protection by the use of resilient seals on joints and rubbing seals on rotating or moving shafts or spindles. Determine dust ingress protection grade according to the enclosure protection grade (IP Code) of GB/T 4208. A method of achieving the required dust ingress protection by specified widths and clearances between joint faces and, in the case of shafts and spindles, specified lengths and diametrical clearances between moving and stationary parts. Determine dust ingress protection grade according to the heat cycling test
Explosive atmosphere - Part 15: Electrical Installations Design, Selection and Erection
爆炸性环境
第15部分：电气装置的设计、选型和安装
1 Scope
This part of “Explosive Atmosphere” contains the specific requirements for the design, selection and erection of electrical installations in hazardous areas associated with explosive atmospheres.
Where the equipment is required to meet other environmental conditions, for example, protection against ingress of water and resistance to corrosion, additional methods of protection may be necessary. The method used shall not adversely affect the integrity of the enclosure.
The requirements of this standard apply only to the use of equipment under normal or near normal atmospheric conditions. For other conditions, additional precautions may be necessary. For example, most flammable materials and many materials which are normally regarded as non-flammable might burn vigorously under conditions of oxygen enrichment. Other precautions might also be necessary in the use of equipment under conditions of extreme temperature and pressure. Such precautions are beyond the scope of this part.
These requirements are in addition to the requirements for installations in non-hazardous areas.
This part applies to all electrical equipment including fixed, portable, transportable and personal, and installations, permanent or temporary.
It applies to installations at all voltages.
This part does not apply to:
—— electrical installations in mines susceptible to firedamp;
Note: This part may apply to electrical installations in mines where explosive gas atmospheres other than firedamp may be formed and to electrical installations in the surface installation of mines.
—— inherently explosive situations and dust from explosives or pyrophoric substances (for example explosives manufacturing and processing);
—— rooms used for medical purposes;
—— electrical installations in areas where the hazard is due to hybrid mixtures of combustible dust and explosive gas, vapour or mist.
This part does not take into account of any risk due to an emission of flammable or toxic gas from the dust.
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 755 Rotating Electrical Machines - Rating and Performance (GB/T 755-2008, IEC 60034-1: 2004, IDT)
GB/T 1408.1 Insulating Materials - Test Methods for Electric Strength - Part 1: Test at Power Frequencies (GB/T 1408.1-2006, IEC 60243-1: 1998, IDT)
GB 3836.1-2010 Explosive Atmospheres – Part 1: Equipment - General Requirements (IEC 60079-0: 2007, MOD)
GB 3836.2-2010 Explosive Atmospheres - Part 2: Equipment Protection by Flameproof Enclosures “d” (IEC 60079-1: 2007, MOD)
GB 3836.3-2010 Explosive Atmospheres - Part 3: Equipment Protection by Increased Safety "e" (IEC 60079-7: 2006, IDT)
GB 3836.4-2010 Explosive Atmospheres - Part 4: Equipment Protection by Intrinsic Safety “i” (IEC 60079-11: 2006, MOD)
GB/T 3836.5-2017 Explosive Atmospheres - Part 5: Equipment Protection by Pressurized Enclosure “p” (IEC 60079-2: 2009, MOD)
GB 3836.6 Electrical Apparatus for Explosive Gas Atmospheres - Part 6: Oil Immersion “o” (GB 3836.6-2004, IEC 60079-6: 1995, IDT)
GB 3836.7 Electrical Apparatus for Explosive Gas Atmospheres - Part 7: Powder Filling “q” (GB 3836.7-2004, IEC 60079-5: 1997, IDT)
GB 3836.8-2014 Explosive Atmospheres - Part 8: Equipment Protection by Type of Protection "n" (IEC 60079-15: 2010, MOD)
GB 3836.9-2014 Explosive Atmospheres - Part 9: Equipment Protection by Type of Protection “m” (IEC 60079-18: 2007, IDT)
GB 3836.13-2013 Explosive Atmospheres - Part 13: Equipment Repair, Overhaul and Reclamation (IEC 60079-19: 2010, MOD)
GB 3836.14-2014 Explosive Atmospheres - Part 14: Classification of Areas - Explosive Gas Atmosphere (IEC 60079-10-1: 2010, IDT)
GB/T 3836.16-2017 Explosive Atmospheres - Part 16: Electrical Installation Inspection and Maintenance (IEC 60079-17: 2007, IDT)
GB 3836.17-2007 Electrical Apparatus for Explosive Gas Atmospheres - Part 17: Construction and Use of Rooms or Buildings Protected by Pressurization
GB/T 3836.18-2017 Explosive Atmospheres - Part 18: Intrinsically Safe Electrical Systems (IEC 60079-25: 2010, MOD)
GB 3836.19-2010 Explosive Atmospheres - Part 19: Fieldbus Intrinsically Safe Concept (FISCO) (IEC 60079-27: 2003, IDT)
GB 3836.20-2010 Explosive Atmospheres - Part 20: Equipment with Equipment Protection Level (EPL) Ga (IEC 60079-26: 2006, IDT)
GB/T 3836.22-2017 Explosive Atmospheres - Part 22: Protection of Equipment and Transmission System using Optical Radiation (IEC 60079-28: 2006, MOD)
GB/T 4208 Degrees of Protection Provided by Enclosure (IP Code) (GB/T 4208-2017, IEC 60529: 2013, IDT)
GB 4793.1 Safety Requirements for Electrical Equipment for Measurement, Control, and Laboratory Use-Part 1: General Requirements (GB 4793.1-2007, IEC 61010-1:2001, IDT)
GB/T 4942.1 Degrees of Protection Provided by the Integral Design of Rotating Electrical Machined (IP Code) - Classification (GB/T 4942.1-2006, IEC 60034-5: 2000, IDT)
GB 4943.1 Information Technology Equipment - Safety - Part 1: General Requirements (GB 4943.1-2011, IEC 60950-1: 2005, MOD)
GB 12476.1-2013 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 1: General Requirements (IEC 61241-0: 2004, MOD)
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 (IEC 60079-10-2: 2009, IDT)
GB 12476.4-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 4: Protection by Intrinsic Safety “iD” (IEC 61241-11: 2005, IDT)
GB 12476.5-2013 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 5: Protection by Enclosures “tD” (IEC 61241-1: 2004, IDT)
GB 12476.6-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 6: Protection by Enclosures “tD” (IEC 61241-18: 2004, IDT)
GB 12476.7-2010 Electrical Apparatus for Use in the Presence of Combustible Dust - Part 7: Type of Protection “pD” (IEC 61241-4: 2001, IDT)
GB 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 (IEC 61241-2-1: 1994, IDT)
GB/T 16895.21-2011 Low-voltage Electrical Installations - Part 4-41: Protection for Safety - Protection Against Electric Shock (IEC 60364-4-41: 2005, IDT)
GB/T 16927.1 High-voltage Test Techniques - Part 1: General Definitions and Test Requirements (GB/T 16927.1-2011, IEC 60060-1:2006, MOD)
GB/T 18380.12 Test on Electric and Optical Fibre Cables under Fire Conditions - Part 12 Test for Vertical Flame Propagation for a Single Insulated Wire or Cable - Procedure for 1kW Pre-mixed Flame (GB/T 18380.12-2008, IEC 60332-1-2: 2004, IDT)
GB/T 19212.7 Safety of Transformers, Reactors, Power Supply Units and Similar Products for Supply Voltages up to 1 100 V - Part 7: Particular Requirements and Test for Safety Isolating Transformers and Power Supply Units Incorporating Saftey Isolating Transformers (GB/T 19212.7-2012, IEC 61558-2-6: 2009,IDT)
GB/T 21714.3-2015 Protection Against Lightning - Part 3: Physical Damage to Structures and Life Hazard (IEC 62305-3: 2010, IDT)
GB/T 29812 Industrial-process Control - Safety of Analyser Houses.
IEC 60079-16 Electrical Apparatus for Explosive Gas Atmospheres - Part 16:Artificial Ventilation for the Protection of Analyzer(s) Houses
3 Terms and Definitions
For the purposes of this document, the terms and definitions given in GB 3836.1-2010 and the following apply.
Note: Additional definitions applicable to explosive atmospheres can be found in GB/T 2900.35-2008.
3.1 general
3.1.1
competent body
individual or organization which can demonstrate appropriate technical knowledge and relevant skills to make the necessary assessments of the safety aspect under consideration
3.1.2
verification dossier
set of documents showing the compliance of electrical equipment and installations
3.2 hazardous areas
3.2.1
hazardous areas
area in which an explosive atmosphere 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: For the purposes of this art, an area is a three-dimensional region or space.
3.2.2
non-hazardous area
area in which an explosive atmosphere is not expected to be present in quantities such as to require special precautions for the construction, installation and use of equipment
3.2.3
group (of an electrical equipment for explosive atmospheres)
classification of electrical equipment related to the explosive atmosphere for which it is to be used
Note: Electrical equipment for use in explosive atmospheres is divided into three groups:
—— group I: electrical equipment for mines susceptible to firedamp;
—— group II (which can be divided into subgroups): electrical equipment for places with an explosive gas atmosphere, other than mines susceptible to firedamp (methane) (see 5.5);
—— group III (which can be divided into subgroups): electrical equipment for places with an explosive dust atmosphere (see 5.5).
3.2.4
maximum permissible surface temperature
highest temperature that a surface of electrical apparatus is allowed to reach in practical service to avoid ignition
Note: The maximum permissible surface temperature will depend upon the type of dust, whether as a cloud or layer, if a layer, its thickness and the application of a safety factor. For details see 5.6.3.
3.2.5
Zones
hazardous areas classified into zones based upon the frequency of the occurrence and duration of an explosive atmosphere
3.2.6
zone 0
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is present continuously or for long periods or frequently
3.2.7
zone 1
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally
3.2.8
zone 2
place in which an explosive atmosphere consisting of a mixture with air of flammable substances in the form of gas, vapour or mist is not likely to occur in normal operation but, if it does occur, will persist for a short period only
Contents of GB/T 3836.15-2017
Foreword I
Introduction V
1 Scope
2 Normative References
3 Terms and Definitions
4 General
5 Selection of Equipment (Excluding Cables and Conduits)
6 Protection from Dangerous (Incendive) Sparking
7 Electrical Protection
8 Emergency Switch-off and Electrical Isolation
9 Wiring Systems
10 Additional Requirements for Type of Protection "d" - Flameproof Enclosures
11 Additional Requirements for Type of Protection "e" - Increased Safety
12 Additional Requirements for Type of Protection "i" - Intrinsic Safety
13 Additional Requirements for Type of Protection 'p" - Pressurized Enclosures
14 Additional Requirements for Type of Protection 'n'
15 Additional Requirements for Type of Protection 'o’ - Oil Immersion
16 Additional Requirements for Type of Protection 'q' - Powder Filling
17 Additional Requirements for Type of Protection 'm’ - Encapsulation
18 Additional Requirements for Type of Protection 'tD' – Protection by Enclosure
Annex A (Normative) Verification of Intrinsically Safe Circuits with More than One Associated Apparatus with Linear Current/Voltage Characteristics
Annex B (Informative) Methods of Determining the Maximum System Voltages and Currents in Intrinsically Safe Circuits with More than One Associated Apparatus with Linear Current/Voltage Characteristics (as Required by Annex A)
Annex C (Informative) Determination of Cable Parameters
Annex D (Informative) Safe Work Procedure Guidelines for Explosive Gas Atmospheres
Annex E (Normative) Potential Stator Winding Discharge Risk Assessment - Ignition Risk Factors
Annex F (Normative) Knowledge, Skills and Competencies of Responsible Persons, Operatives and Designers
Annex G (Informative) Examples of Dust Layers of Excessive Thickness
Annex H (Normative) Frictional Sparking Risks with Light Metals and Their Alloys
Annex I (Informative) Introduction of an Alternative Risk Assessment Method Encompassing “Equipment Protection Levels” for Ex Equipment
Bibliography
