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Basic Principles of Explosion Prevention Concept of Explosion Explosion is when a substance suddenly changes from one state to another state after physical or chemical changes, and releases huge amounts of energy. The energy released at a rapid speed will cause violent impact and damage to surrounding objects. Three conditions must be met for an explosion to occur: 1) Explosive substances: Substances that react with oxygen (air), including gases, liquids, and solids. (gas: Hydrogen, acetylene, methane, etc. ； liquid: alcohol, gasoline ； solid: Dust, fiber dust, etc. )2)Oxygen: Air. 3) Ignition source: Including open flames, electrical sparks, mechanical sparks, electrostatic sparks, high temperatures, chemical reactions, light energy, etc. Why explosion-proof and flammable substances are needed: Many production sites produce certain flammable substances. About two-thirds of the places underground in coal mines contain explosive substances ； In the chemical industry, more than 80% of production workshop areas contain explosive substances. Oxygen: Oxygen is everywhere in the air. Ignition source: A large number of electrical instruments are used in the production process. Various friction sparks, mechanical wear sparks, static sparks, high temperatures, etc. are inevitable, especially when instruments and electrical failures occur. Objectively speaking, many industrial sites meet explosion conditions. When the mixed concentration of explosive substances and oxygen is within the explosion limit range, if an explosion source exists, an explosion will occur. Therefore, it is necessary to take explosion protection. Principles of explosion-proof instruments and classification of hazards in hazardous places: Explosive Substances Area Definition Chinese Standard North American Standard Zone 0: Div.1 Gas (CLASS Ⅰ) Under normal circumstances, places where explosive gas mixtures exist continuously or for a long time Zone 1: Places where explosive gas mixtures may appear under normal circumstances Zone 1 Zone 2: Div.2 Places where explosive gas mixtures are unlikely to appear under normal circumstances, but only occur occasionally or for a short period of time under abnormal circumstances. Zone 10 Div.1: Dust or fiber (CLASS Ⅱ/Ⅲ) Under normal circumstances, the mixture of explosive dust or combustible fiber and air may appear continuously, frequently in a short time or exist for a long time 11 Zone Div.2: Under normal circumstances, explosive dust or a mixture of combustible fibers and air cannot appear, but only appears occasionally or for a short period of time under abnormal circumstances. Applicability of explosion-proof methods to hazardous places: Serial number explosion-proof type code * * Applicable zones for standard explosion-proof measures 1 Flameproof type d GB3836.2 Isolate existing ignition sources Zone1, Zone2 2 Increased safety type e GB3836.3 Try to prevent the generation of ignition sources Zone1, Zone2 3 Intrinsic safety type ia GB3836.4 Limit the energy of ignition sources Zone0-2 Intrinsic safety type ib GB3836.4 Limit the energy of ignition sources Zone1, Zone2 4 Positive pressure type p GB3836.5 Separate hazardous substances from ignition sources Zone1, Zone2 5 Oil-filled type o GB3836.6 Separate hazardous substances from ignition sources Zone1, Zone2 6 Sand-filled type q GB3836.7 Separate hazardous substances from ignition sources Zone1, Zone2 7 Non-sparking type n GB3836.8 Try to prevent the generation of ignition sources Zone2 8 Casting type m GB3836.9 Try to prevent the generation of ignition sources Zone1, Zone2 9 Air-tight type h GB3836.10 Try to prevent the generation of ignition sources Zone1, Zone2 Applicability of explosion-proof to hazardous places: The classification of explosive hazardous gases is based on the minimum spark energy that may detonate. my country, Europe and most of the world * * and regions divide explosive gases into four hazard levels, as shown in the table below: Working condition category Gas classification Representative gas Minimum detonation spark energy Undermine I Methane 0.280mJ Factory outside the mine IIA Propane 0.180mJ IIB Ethylene 0.060mJ IIC Hydrogen 0.019mJ The United States and Canada first divided explosive objects scattered in the air into three CLASS: CLASS ⅠGas and vapor; CLASS Ⅱ dust; CLASS Ⅲfiber. Then gas and dust are divided into Group (group) : Group name Representative gas or dust A Acetylene B Hydrogen C Ethylene D Propane E Metal dust F Coal dust G Grain dust gas temperature group division: Common explosive gases with surface temperature of safe objects in the temperature group T1 ≤ 450℃ 46 types of T2 such as hydrogen and acrylonitrile ≤ 300℃ 47 types of T3 such as acetylene and ethylene ≤ 200℃ 36 types of T4 such as gasoline and crotonaldehyde ≤ 135℃ 6 types of T5 such as acetaldehyde and tetrafluoroethylene ≤ 100℃ Carbon disulfide T6 ≤ 85℃ The meaning of the explosion-proof mark Ex(ia)ⅡC T6 for ethyl nitrate and ethyl nitrite instruments: Mark content Symbol meaning Explosion-proof statement Ex conforms to certain explosion-proof standards, such as my country's * * Standard explosion-proof method ia Uses ia-level intrinsically safe explosion-proof method and can be installed in zone 0. Gas category IIC is allowed to involve Class ⅡC explosive gas temperature group T6. The surface temperature of the instrument does not exceed 85°C. Ex(ia)ⅡC meaning. Symbol content. Symbol meaning. Explosion-proof statement Ex. Complies with European explosion-proof standards. Explosion-proof method ia uses ia-level intrinsically safe explosion-proof method. Explosive gases: Note: There is no temperature group item in this mark, indicating that the instrument is not in direct contact with explosive gases. Explosion-proof terms: Definitions of explosion-proof terms and standard safety barrier safety parameters: * 8226; Maximum allowable voltage of safety barrier: Um guarantees the intrinsically safe performance of the intrinsically safe end of the safety barrier and allows the highest possible input voltage at the non-intrinsically safe end. * 8226; Maximum open circuit voltage of safety barrier: Uoc The maximum voltage when the intrinsically safe terminal is open-circuited within the maximum allowable voltage range * 8226; Maximum short-circuit current of safety barrier: Isc The maximum current value when the intrinsically safe terminal is short-circuited within the maximum allowable voltage range * 8226; Safety barrier allows distributed capacitance: Ca is the maximum allowable external capacitance of the intrinsically safe terminal when ensuring intrinsic safety performance. * 8226; Safety barrier allows distributed inductance: La Explanation of the format of the explosion-proof mark for the maximum allowable external inductor at the intrinsically safe end while ensuring intrinsic safety performance: Scientifically classify and classify the explosive hazardous media in factories or mining areas according to their ignition energy, minimum ignition temperature, and the time period during which explosive hazardous gases exist on site to determine the explosion-proof signs and explosion-proof forms of on-site explosion-proof equipment. Explosion-proof mark format: Ex (ia) ⅡC T4 Explosion-proof mark Explosion-proof level Gas group Temperature group Explosion-proof level description: ia level: Electrical equipment that cannot ignite explosive gas mixtures during normal operation, one fault, or two faults. During normal operation, the safety factor is 2.0 ； When a fault occurs, the safety factor is 1.5 ； When there are two faults, the safety factor is 1.0. Note: Contacts with sparks must be equipped with flameproof enclosures, airtight enclosures or double the safety factor. Class ib: Electrical equipment that cannot ignite explosive gas mixtures during normal operation and during a fault. During normal operation, the safety factor is 2.0 ； In case of a fault, the safety factor is 1.5. During normal operation, the sparking contacts must be protected by a flameproof shell or an airtight shell, and there are measures for self-display of faults. The safety factor for one fault is 1.0.