1.0.1 This code is formulated with view to standardizing the design of electrical installations in explosive atmospheres, implementing the guideline of "prevention first" when designing, ensuring human and property safety, and taking precaution measures according to specific conditions.
1.0.2 This code is applicable to the classification of hazardous areas and design of electrical installations for new construction, extension and renovation, for which explosive atmospheres may occur in the process of producing, processing, handling, transporting and storing.
This code is not applicable to the following atmospheres:
1 In the pit;
2 During manufacturing, using or storing gunpowder, explosive and initiating explosive, fuze and initiating explosive devices, etc.;
3 At places with electrical installations for electrolysis and electroplating which make use of electric energy in production and directly associate with the production process;
4 With materials which may fire voluntarily by using strong oxidizer while without an external ignition source;
5 With vehicles for water, land and air transportation and with offshore and on-land oil well platforms;
6 With piping systems for heating, air conditioning, cooking, washing and the similar while adopting flavored gas as the fuel;
7 In the treatment room;
8 With catastrophic failure.
1.0.3 The code considers nothing about influence on classification of hazardous area and on design of relevant electrical installations casused by indirect harms.
1.0.4 Classification of hazardous areas shall be jointly completed by professional staff in charge of processing medium properties, equipment and processing properties in production process and engineering technicians in safety and electrical disciplines through consultation.
1.0.5 In addition to the requirements stipulated in this code, those stipulated in the current relevant standards in China shall be complied with for the design of electrical installations in explosive atmospheres.
2 Terminologies
2.0.1 Flash point
The lowest liquid temperature, at which with enough vapors released from liquid to form flammable gas or air mixture standard conditions.
2.0.2 Ignition temperature
The minimum temperature, at which ignition occurs at the hot surface of mixture formed by flammable gas or vapor together with air, under specified conditions.
2.0.3 Ambient temperature
The average maximum temperature of the hottest months in past years at the designated area.
2.0.4 Flammable material
Refer to substance that is flammable and is able to generate flammable gas, vapor or mist.
2.0.5 Flammable gas or vapor
The gas or vapor that is able to form an explosive gas atmosphere when being mixed with air in a certain proportion.
2.0.6 Flammable liquid
The liquid that is able to generate flammable vapor under foreseeable application conditions.
2.0.7 Flammable mist
The droplet of flammable liquid that is able to form an explosive atmosphere when volatilizing.
2.0.8 Explosive gas mixture
Mixture of gas, vapor, or mistlike flammable material mixed with air in atmospheric conditions, of which the combustion after ignition may spread within the full range.
2.0.9 Highly volatile liquid
Highly volatile liquid refers to the one with absolute vapor pressure exceeding 276 kPa at 37.8 ℃, including butane, ethane, ethylene, propane and propylene, etc. as well as liquefied natural gas, natural gas liquids and their mixtures.
2.0.10 Explosive gas atmosphere
An atmosphere that may keep combustion spreading freely under atmospheric conditions after the mixture of flammable gas or vapor subtance and air is ignited.
2.0.11 Explosive limit
1 Lower explosion limit (LEL)
The minimum concentration of flammable gas, vapor or mist to form explosive gas mixture in the air. When the concentration of flammable gas or vapor in the air is lower than that, the gas atmosphere will not generate explosion.
2 Upper explosion limit (UEL)
The maximum concentration of flammable gas, vapor or mist in the air to form explosive gas mixture. When the concentration of flammable gas or vapor in the air exceeds that, the gas atmosphere will not generate explosion.
2.0.12 Hazardous area
The area where preventive measures required shall be taken for the structure, installation and application of electrical equipment due to the quantity of explosive mixture that may appear or expect to appear is sufficient.
2.0.13 Non-hazardous area
The area where preventive measures required shall not be taken for the structure, installation and application of electrical equipment due to the quantity of explosive mixture that may appear or expect to appear is insufficient.
2.0.14 Zone
The full or a part of hazardous area. According to the occurence frequency and duration of explosive mixture, the area may be classified into several zones with different hazard level.
2.0.15 Source of release
The position or place where may release substances to form explosive mixture.
2.0.16 Natural ventilation atmosphere
The zone where fresh air may replace original mixture due to the influence of natural wind or temperature difference.
2.0.17 Artificial ventilation atmosphere
The zone where the orginal mixture is replaced by fresh air by virtue of device application, such as a fan or exhauster.
2.0.18 Normal operation
The operation condition of equipment within the range of its design parameters.
2.0.19 Dust
Small solid particles which are precipitable in the air due to their own weights and may also keep suspending in the air for a certain period, including fibre and flyings as well as dust and fine particles specified in the current national standard "Specifications for Bag House" (GB/T 6719).
2.0.20 Combustible dust
Dust, fibre or flyings that may generate combustion or flameless combustion in the air and may form explosive mixture at the barometric pressure and normal temperature.
2.0.21 Conductive flyings
Solid particles with the nominal size larger than 500 μm, which may suspend in the air and may also be precipitable due to their own weights, including firbre.
2.0.22 Conductive dust
The dust with resistivity equals to or less than 1×103Ω?m.
2.0.23 Non-conductive dust
The dust with resistivity larger than 1×103Ω?m.
2.0.24 Explosive dust atmosphere
An atmosphere that may keep combustion spreading freely under atmospheric conditions after the mixture of combustible dust and air is ignited.
2.0.25 Heavier-than-air gases or vapors
Gases or vapors with the relative density larger than 1.2.
2.0.26 Lighter-than-air gases or vapors
Gases or vapors with the relative density less than 0.8.
2.0.27 Ignition temperature of dust layer
The minimum temperature of the hot surface on which ignition of dust layer with specified thickness occurs.
2.0.28 Ignition temperature of dust cloud
The minimum temperature of inner wall of furnace, in which the dust cloud in furnace air ignites.
2.0.29 Explosive atmospheres
An atmosphere that may keep combustion spreading freely under atmospheric conditions after the mixture of gas, vapor, dust, mist, fibre or flyings and air is ignited.
2.0.30 Equipment protection level (EPL)
The protection level specified for equipment according to the possibility of equipment to be a source of ignition, and different features of explosive gas atmosphere and explosive dust atmosphere.
3 Explosive Gas Atmosphere
3.1 General Requirement
3.1.1 When one of the following explosive gas mixture atmospheres occurs or may occur in the process of manufacturing, processing, handling, transporting or storing, design of electrical installations in explosive gas atmosphere shall be made:
1 Under atmospheric conditions, the explosive gas mixture is formed due to the mixing of flammable gas and air;
2 The explosive gas mixture is formed by vapor or mist of flammable liquid through mixing with air, of which the flash point is less than or equal to the ambient temperature;
3 In the case that the operation temperature of material is higher than the flash point of flammable liquid, and when the flammable liquid has the potential leakage, explosive gas mixture is formed due to mixing of vapor or mist of flammable liquid and air.
3.1.2 In the explosive gas atmosphere, the conditions for explosion shall meet the following conditions:
1 With flammable gas and vapor or mist of flammable liquid, and the concentration is within the explosive limit;
2 With spark, arc or high temperature that is able to ignite the explosive gas mixture.
3.1.3 The following explosion-proof measures shall be taken in explosive gas atmosphere:
1 The occurring possibility of explosion conditions simultaneously shall be minimized.
2 In process design, the following measures to eliminate or reduce the release and accumulation of flammable materials shall be taken:
1) In the process flow, a lower pressure and temperature shall be adopted to limit the flammable materials into a closed container;
2) The process layout shall be able to limit and reduce the range of hazardous area; and hazardous area of different levels or the hazardous area and non-hazardous area shall be separated in a respective plant or within the battery limit;
3) In equipment, nitrogen or other inert gases may be adopted for covering;
4) Measures such as safety interlocking or adding chemical reagents into as polymerization inhibitor for the polymerization reaction in trouble shall be taken.
3 To prevent explosive gas mixture from generating or to shorten the detention time of explosive gas mixture, the following measures may be taken:
1) The process unit should have outdoor and open type arrangement;
2) Set artificial ventilation devices;
3) Set a plenum in explosive atmospheres;
4) Automatic measurer or device shall be arranged at places where explosive gas mixture is prone to form or accumulate, and the instrument shall be able to reliably send signals or cut the power off when the gas or vapor concentration is close to 50% of the explosive limit.
4 In an area, measures to eliminate or control spark, arc or high temperature generated by the line shall be taken.
