GB 50058-2014Code for design of electrical installations in explosive atmospheres (English PDF)

1.0.4 Classification of explosive hazardous areas shall be negotiated to complete

jointly by professional personnel who are in charge of production technology processing media properties, equipment and processing properties and engineering technical personnel who are in charge of safety and electrical engineering.

1.0.5 Besides conforming to the Code, design of electrical installations in explosive

atmosphere shall also comply with the provisions of existing related national standards.

2.0.1 Flash point

Minimum liquid temperature that the amount of making liquid become vapor can form flammable gas or air mixture under standard conditions.

2.0.2 Ignition temperature

Minimum temperature that mixture of flammable gas or vapor is ignited by hot surface under specified conditions.

2.0.3 Ambient temperature

Referring to the average maximum temperature of the hottest months over years in designated area.

2.0.4 Flammable material

Referring to that the material itself is flammable and can produce flammable gas, vapor or mist.

2.0.5 Flammable gas or vapor

Gas or vapor that will form an explosive gas atmosphere after mixing with air at a certain percentage.

2.0.6 Flammable liquid

Liquid that can produce flammable vapor or mist under the foreseeable conditions of use.

2.0.7 Flammable mist

Flammable liquid droplets that form an explosive atmosphere by volatile in the air.

2.0.8 Explosive gas mixture

Under atmospheric conditions, combustion will spread over the whole scope after mixture of gas, vapor or mist-like flammable material and air is ignited.

2.0.9 Highly volatile liquid

Highly volatile liquid refers to the liquid that absolute vapor pressure exceeds 276 kPa at a temperature of 37.8 °C. These liquids include butane, ethane, ethylene, propane, propylene, liquefied natural gas, natural gas liquids and their mixture.

2.0.10 Explosive gas atmosphere

The environment that mixture of gas or vapor can spread combustion voluntarily after being ignited under atmospheric conditions.

2.0.11 Explosive limit

2.0.12 Hazardous area

The area that the quantity of existing explosive mixture or expected quantity of existing explosive mixture is sufficient to take precautionary measures for the structure, erection and use of electrical equipment.

2.0.13 Non-hazardous area

The area where the quantity of existing explosive mixture is insufficient to take precautionary measures for the structure, erection and use of electrical equipment.

2.0.14 Area

All or part of explosive hazardous area. It can be classified into several areas in different degrees of danger according to the emerging frequency and duration of explosive mixture.

2.0.15 Source of release

Position or location of the material that can form explosive mixture.

2.0.16 Natural ventilation atmosphere

The area where fresh air can replace the original mixture due to the role of natural wind or temperature difference.

2.0.17 Artificial ventilation atmosphere

The area where air fan, exhaust fan and other installations are used to replace original mixture with fresh air.

2.0.18 Normal operation

Refer to the operating conditions of equipment within the range of design parameters.

2.0.22 Conductive dust

Dust that resistivity is equal to or less than 1×103 ohm·m.

2.0.23 Non-conductive dust

Dust that resistivity is greater than 1×103 ohm·m.

2.0.24 Explosive dust atmosphere

Under atmospheric conditions, the environment that can keep voluntary spread of burning after the mixture of combustible dust and air is ignited.

2.0.25 Heavier-than-air gases or vapors

Gas or vapor that relative density is greater than 1.2.

2.0.26 Lighter-than-air gases or vapors

Gas or vapor that relative density is less than 0.8.

2.0.27 Ignition temperature of dust layer

Minimum temperature of hot surface where dust layer with stipulated thickness is ignited.

3.1 General requirement

3.1.1 There shall be design of electrical installations in explosive gas atmosphere when

one of the following explosive gas mixture atmospheres occurs or probably occurs during production, processing, handling, transshipping or storage process.

3.1.2 Explosion in an explosive atmosphere shall comply with the following conditions.

3.2.2 It may be classified as non-explosive hazardous area when meeting one of the following conditions.

3.2.3 Source of release shall be classified into continuous-grade source of release, first-grade source of release and second-grade source of release according to release frequency and duration of flammable material. Grading of source of release shall meet the following requirements.

3.3 Extension of hazardous area in explosive gas atmosphere

3.3.1 Extension of hazardous area for explosive gas atmosphere shall be determined

according to the following requirements.

3.3.2 Grade and extension of explosive hazardous areas shall follow the provisions in Annex A of this Code and is determined according to the release amount, release rate, boiling point, temperature, flash point, relative density, lower explosive limit, obstacles and other conditions in combination with practical experience.

3.3.3 When the workshop in explosive gas atmosphere cannot form explosive gas

atmosphere after adopting positive pressure or continuous ventilation dilution measures, the workshop may be reduced to a non-explosive hazardous environment.

Air source introduced through ventilation shall be safe and reliable and has no flammable material, corrosive media and mechanical impurities; air inlet shall be 1.5 m higher than the extension of explosive area classified.

3.3.4 Design of electrical installations in explosive gas atmosphere shall include

explosion hazard zoning map; simple or small plants may be expressed through literal statement.

3.4 Grading and grouping of explosive gas mixture

4.1 General requirement

4.1.1 When explosive dust mixture formed by air and dust that occur or may occur

during production, processing, transshipment or storage process, design of electrical installations in explosive dust atmosphere shall be carried out.

4.1.2 Dust in explosive dust environment may be classified into the following three

grades.

4.1.4 The following measures to prevent an explosion shall be adopted in explosive dust environments.

4.2 Classification of hazardous area in explosive dust atmosphere

4.2.1 Dust source of release shall be classified into continuous-grade source of release, first-grade source of release and second-grade source of release according to release frequency and duration of explosive dust. Source of release shall meet the following requirements.

4.2.2 Explosive hazardous area shall be classified into area 20, area 21 and area 22

based on the frequency of explosive dust environment and duration; areas shall comply with the following provisions.

4.3 Extension of hazardous area in explosive dust atmosphere

4.3.1 Under normal circumstances, extension shall be determined through evaluating

the possibility that the grade of source of release involving this environment causes explosive dust atmosphere.

4.3.2 Extension of area 20 mainly includes the interior area of pipes and production

and processing equipment where dust cloud generates continuously. When the outside of dust container continuously has explosive dust environment, it may be classified as area 20.

4.3.4 Extension of area 22 shall be determined according to the following provisions.

1 For the places formed by second-grade source of release, area scope shall be

4.3.5 Typical example drawing on extension of hazardous area in explosive dust

atmosphere shall comply with the provisions in Annex D of this Code.

4.3.6 Examples of flammable dust shall comply with the provisions in Annex E of this

Code.

5.1 General requirement

5.1.1 The electrical installations in explosive atmosphere shall be designed in accordance with the following regulations.

5.2 Selection of electrical equipment in explosive atmosphere

5.2.1 In the explosive atmosphere, the selection of electrical equipment shall consider the following factors.

5.3 Erection of electrical equipment in explosive atmosphere

5.3.1 Oil-immersed type equipment shall be used on the condition that there is no

vibration or inclination and the installation condition is stable.

5.3.2 If non-explosion protection equipment is used as cross-wall mechanical

transmission, the following regulations shall be met.

5.3.3 In addition to intrinsic safe circuit, the circuit and equipment in the explosive atmosphere shall be installed with overload, short-circuit and grounding protection devices. As to the equipment which is impossible to have overload problem, it is not necessarily to be installed with overload protection device.

5.3.4 Under emergency circumstance, take one or more measures at the appropriate

site beyond the boundary of the hazardous area to turn off the equipment in the hazardous area. The continuously operating equipment is not included in the emergency shutdown circuit. The equipment shall be installed in the independent circuit to prevent additional possible hazards.

5.3.5 Substation, distribution substation and control room shall be designed in accordance with the following regulations.

5.4 Design of electrical wiring in explosive atmosphere

5.4.1 Cable and wire in the explosive atmosphere shall be selected in accordance with the following regulations.

5.4.2 The circuit in the explosive atmosphere shall be protected in accordance with the following regulations.

5.4.3 The electrical wire in the explosive atmosphere shall be installed in accordance with the following regulations.

5.5 Grounding design in explosive atmosphere

5.5.3 The protective grounding of the electrical equipment in the explosive atmosphere shall conform to the following regulation.

5.5.4 The grounding device of equipment shall be separated from the grounding device of independent lightning rod which prevents direct lightning. It can be amalgamated with the lightning rod installed on the building which prevents direct lightning. It can also be amalgamated with the grounding device which prevents lightning induction.

Select the device with the lowest grounding resistance value.

5.5.5 Metal parts in Area 0 and 20 are not appropriate to adopt cathodic protection. If

cathodic protection is used, special design shall be adopted. Insulated parts requiring for cathodic protection shall be installed outside the explosive atmosphere.