Classification of explosive hazardous substances

Explosive substances are divided into three categories in China:

Class I: mine methane;

Class II: explosive gas mixture (including vapor and mist);

Class III: explosive dust and fiber.

Basic conditions of explosion

1) explosive substances: A substance that reacts with oxygen (air), Including gases, liquids and solids.

◎ gas: hydrogen, Acetylene, Methane, etc;

◎ liquid: alcohol, Gasoline;

◎ solid: dust, Fiber dust, etc.

Air / oxygen.

Ignition source: Including open fire, electrical spark, mechanical spark, electrostatic spark, high temperature, chemical reaction, light energy, etc.

2) necessary conditions for explosion-proof explosion:

Avoid explosive atmospheres:

◎ prevent possible explosion caused by explosive and flammable substances in chemical plants and refineries;

◎ explosive or flammable substances escape from equipment and pipelines due to poor sealing;

◎ 消除可能的Ignition source:遇到仪表的电气接点和电气设备短路时形成的火花， May cause explosion or combustion.

Division of hazardous areas

Gas environment:

China is the same as IEC standard, Explosive gas hazardous areas can be divided into three areas, Zone 0, zone 1 and zone 2. The corresponding definitions are as follows:

◎ zone 0: under normal conditions, Explosive gas always exists or exists for a long time; Areas with continuous hazards greater than 1000 hours / year;

◎ zone 1: flammable gas may occur or exist during the proper operation of the instrument; Areas with intermittent hazards of 10 ~ 1000 hours / year;

◎ zone 2: generally, There is no flammable gas and even if it occurs occasionally, Its existence time is also very short; Area with hazard of 0.1 ~ 10 hours / year under accident condition;

Non hazardous area (less than 1 hour / year)

Dust environment:

For dusty locations, According to the frequency and duration of combustible dust / air mixture and the thickness of dust layer, it is divided into the following three areas, Zones 20, 21 and 22.

◎ zone 20: combustible dust occurs continuously or frequently during normal operation, Places where the quantity is enough to form a mixture of combustible dust and air and / or may form an uncontrollable and extremely thick dust layer;

◎ zone 21: during normal operation, Places where there may be enough dust to form a mixture of combustible dust and air but are not classified as zone 20;

◎ zone 22: under abnormal conditions, Places where combustible dust clouds occur occasionally and exist only for a short time, or combustible dust accumulates occasionally or there may be a dust layer and produce combustible dust air mixture.

Class I: electrical equipment for coal mine

Class II: electrical equipment for explosive environment other than coal mine, According to the characteristics of explosive gas, Flameproof and intrinsically safe electrical equipment are divided into IIA, IIb and IIC.

The equipment marked IIB can be applicable to the service conditions of IIA equipment; The equipment marked iic can be applied to the service conditions of IIA and IIB.