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The concept of explosion: An explosion occurs when a substance, through physical or chemical changes, suddenly changes from one state to another, releasing a large amount of energy. The energy released from such rapid speed will cause intense impact and damage to the objects around it. Three conditions that must be present for an explosion: 1) Explosive material: a substance that can react with oxygen (air), including gases, liquids, and solids. (Gases: hydrogen, acetylene, methane, etc.) ； Liquids: alcohol, gasoline ； Solids: dust, fibrous dust, etc. ) 2 ) Oxygen: Air. 3) Ignition sources: include open flames, electrical sparks, mechanical sparks, static electricity sparks, high temperatures, chemical reactions, light energy, etc. Why is explosion protection needed? Flammable substances: Many production sites generate certain flammable materials. About two-thirds of coal mine sites have explosive materials present ； In the chemical industry, explosive substances are present in over 80% of the production facilities. Oxygen: Oxygen is present everywhere in the air. Ignition sources: During the production process, electrical instruments are used in large quantities, and electrical sparks resulting from friction, sparks caused by mechanical wear, static electricity sparks, and high temperatures are inevitable, especially when the instruments or electrical systems malfunction. Objectively, many industrial sites meet the conditions for explosion. When the mixture concentration of explosive substances and oxygen is within the explosive limit range, an explosion will occur if there is an ignition source. Therefore, it is necessary to adopt explosion protection. Principle of instrument explosion protection. Classification of hazard levels in hazardous areas: Definition of explosive substance zones – Chinese standards and North American standards. Gases (CLASS I): Areas where explosive gas mixtures exist continuously or for extended periods under normal conditions. Zone 0, Div.1; Areas where explosive gas mixtures may occur under normal conditions. Zone 1; Areas where explosive gas mixtures cannot occur under normal conditions, but only occasionally or for short periods under abnormal conditions. Zone 2, Div.2. Dusts or fibers (CLASS II/III): Areas where explosive dusts or combustible fibers mixed with air may exist continuously, frequently for short periods, or for extended periods under normal conditions. Zone 10, Div.1; Areas where such mixtures cannot occur under normal conditions, but only occasionally or for short periods under abnormal conditions. Zone 11, Div.2. Applicability of explosion protection methods to hazardous areas: Serial number, code for explosion protection type **, standard, explosion protection measures, applicable areas. 1. Flameproof type d, GB3836.2 – Isolates ignition sources; Zones 1, Zone 2. 2. Increased safety type e, GB3836.3 – Prevents the generation of ignition sources; Zones 1, Zone 2. 3. Intrinsic safety type ia, GB3836.4 – Limits the energy of ignition sources; Zones 0–2. Intrinsic safety type ib, GB3836.4 – Limits the energy of ignition sources; Zones 1, Zone 2. 4. Positive pressure type p, GB3836.5 – Separates hazardous substances from ignition sources; Zones 1, Zone 2. 5. Oil-immersed type o, GB3836.6 – Separates hazardous substances from ignition sources; Zones 1, Zone 2. 6. Sand-filled type q, GB3836.7 – Separates hazardous substances from ignition sources; Zones 1, Zone 2. 7. Spark-free type n, GB3836.8 – Prevents the generation of ignition sources; Zone 2. 8. Sealed type m, GB3836.9 – Prevents the generation of ignition sources; Zones 1, Zone 2. 9. Hermetically sealed type h, GB3836.10 – Prevents the generation of ignition sources; Zones 1, Zone 2. Classification of explosive gases: Based on the minimum spark energy required to initiate an explosion, China, Europe, and most other countries classify explosive gases into four hazard levels, as shown in the table below. Operating condition category, gas classification, representative gases, minimum ignition spark energy. Underground mines: Class I, methane – 0.280 mJ. Factories outside mines: Class IIA, propane – 0.180 mJ; Class IIB, ethylene – 0.060 mJ; Class IIC, hydrogen – 0.019 mJ. The United States and Canada first classified explosive substances dispersed in air into three classes: CLASS I for gases and vapors; CLASS II for dusts; CLASS III for fibers. Gases and dusts are further divided into groups: Group name, representative gases or dusts. A, acetylene; B, hydrogen; C, ethylene; D, propane; E, metal dusts; F, coal dusts; G, grain dusts. Classification of gas temperature groups: Temperature group, safe object surface temperature, common explosive gases. T1 ≤ 450°C, hydrogen, acrylonitrile, etc. – 46 types. T2 ≤ 300°C, acetylene, ethylene, etc. – 47 types. T3 ≤ 200°C, gasoline, butyraldehyde, etc. – 36 types. T4 ≤ 135°C, acetaldehyde, tetrafluoroethylene, etc. – 6 types. T5 ≤ 100°C, carbon disulfide. T6 ≤ 85°C, ethyl nitrate and ethyl nitrite. Meaning of the explosion protection mark Ex(ia)IICT6: Mark content, symbol meaning. Explosion protection statement: Ex – Complies with a certain explosion protection standard, such as China’s standards. Explosion protection method: ia – Uses an ia-level intrinsic safety explosion protection method; can be installed in Zone 0. Gas category: IIIC – Allows exposure to IIIC-class explosive gases. Temperature group: T6 – The surface temperature of the instrument does not exceed 85°C. Meaning of Ex(ia)IICT6: Mark content, symbol meaning. Explosion protection statement: Ex – Complies with European explosion protection standards. Explosion protection method: ia – Uses an ia-level intrinsic safety explosion protection method; can be installed in Zone 0. Gas category: IIIC – Allows exposure to IIIC-class explosive gases. Note: The absence of a temperature group in this mark indicates that the instrument does not come into direct contact with explosive gases. Explosion protection terminology: Related terms and standards for explosion protection. Definitions of safety barrier parameters: Maximum allowable voltage of the safety barrier, Um – The highest voltage allowed at the intrinsically safe terminal to ensure its intrinsic safety performance; Maximum open-circuit voltage of the safety barrier, Uoc – The maximum voltage when the intrinsically safe terminal is open within the maximum allowable voltage range; Maximum short-circuit current of the safety barrier, Isc – The maximum current when the intrinsically safe terminal is short-circuited within the maximum allowable voltage range; Maximum allowable distributed capacitance of the safety barrier, Ca – The maximum external capacitance allowed at the intrinsically safe terminal while maintaining intrinsic safety performance; Maximum allowable distributed inductance of the safety barrier, La – The maximum external inductance allowed at the intrinsically safe terminal while maintaining intrinsic safety performance. Explanation of the format of explosion protection marks: Hazardous explosive substances in factories or mining areas are scientifically classified and graded based on their ignition energy, minimum ignition temperature, and the duration of presence of explosive gases in the area, so as to determine the explosion protection mark and type required for the explosion protection equipment used there. Explosion protection mark format: Ex (ia) IIIC T4. The explosion protection rating, gas group, and temperature group are indicated here. Explanation of the explosion protection rating: Class ia: Electrical equipment that cannot ignite explosive gas mixtures under normal operating conditions, as well as in the presence of one or two faults. During normal operation, the safety factor is 2.0 ； In the event of a failure, the safety factor is 1.5 ； For two failures, the safety factor is 1.0. Note: Contacts that generate sparks must be equipped with an explosion-proof enclosure, a hermetically sealed enclosure, or the safety factor must be doubled. IB rating: Electrical equipment that cannot ignite explosive gas mixtures under normal operation and in the presence of a fault. During normal operation, the safety factor is 2.0 ； In the event of a failure, the safety factor is 1.5. During normal operation, contacts that generate sparks must be protected by an explosion-proof or airtight enclosure, and measures for automatic fault indication must be in place; the safety factor in the event of a fault is 1.0.