Explosion protection rating classification
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Classification of Explosion Protection GradesI. Classification of Hazardous Areas: Explosive Substances
Area Definitions
Chinese Standards
North American Standards
Gases
CLASS I: Areas where explosive gas mixtures are present 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 may appear occasionally or for short periods only under abnormal conditions
Zone 2, Div.2
Dusts
CLASS II
Fibers
CLASS III: Areas where explosive dusts or combustible fibers mixed with air may be present continuously, frequently for short periods, or for extended periods under normal conditions
Zone 10, Div.1: Areas where explosive dusts or combustible fibers mixed with air cannot occur under normal conditions, but may appear occasionally or for short periods only under abnormal conditions
Zone 11, Div.2
II. Applicability of Explosion Protection Methods to Hazardous Areas:
Serial Number | Explosion Protection Type | Code | Standard | Explosion Protection Measures | Applicable Areas
1 | Flameproof type | d | GB3836.2 | Isolate ignition sources | Zone 1, Zone 2
2 | Increased safety type | e | GB3836.3 | Prevent the generation of ignition sources | Zone 1, Zone 2
3 | Intrinsic safety type | ia | GB3836.4 | Limit the energy of ignition sources | Zone 0, Zone 2; Intrinsic safety type ib | GB3836.4 | Limit the energy of ignition sources | Zone 1, Zone 2
4 | Positive pressure type | p | GB3836.5 | Separate hazardous substances from ignition sources | Zone 1, Zone 2
5 | Oil-immersed type | o | GB3836.6 | Separate hazardous substances from ignition sources | Zone 1, Zone 2
6 | Sand-filled type | q | GB3836.7 | Separate hazardous substances from ignition sources | Zone 1, Zone 2
7 | Spark-free type | n | GB3836.8 | Prevent the generation of ignition sources | Zone 2
8 | Sealed type | m | GB3836.9 | Prevent the generation of ignition sources | Zone 1, Zone 2
9 | Hermetically sealed type | h | GB3836.10 | Prevent the generation of ignition sources | Zone 1, Zone 2
III. Applicability of Explosion Protection to Hazardous Areas: Classification of Explosive Gases
Based on the minimum spark energy required to initiate an explosion, China, Europe, and most other countries and regions 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 | Ⅰ | Methane | 0.280 mJ
Factories outside mines | ⅡA | Propane | 0.180 mJ
| ⅡB | Ethylene | 0.060 mJ
| ⅡC | Hydrogen | 0.019 mJ
IV. Classification of Gas Temperature Groups:
Temperature Group | Safe Surface Temperature of Objects | 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
V. Meaning of the Explosion Protection Marking Ex(ia)ⅡC T6:
Marking Content | Symbol | Meaning
Explosion protection declaration | Ex | Complies with a certain explosion protection standard, such as China’s standards
Explosion protection method | ia | Uses the ia-level intrinsic safety explosion protection method; can be installed in Zone 0
Gas category | ⅡC | Permitted to operate in environments with ⅡC-class explosive gases
Temperature group | T6 | The surface temperature of the instrument does not exceed 85°C
Meaning of Ex(ia)ⅡC:
Marking Content | Symbol | Meaning
Explosion protection declaration | Ex | Complies with European explosion protection standards
Explosion protection method | ia | Uses the ia-level intrinsic safety explosion protection method; can be installed in Zone 0
Gas category | ⅡC | Permitted to operate in environments with ⅡC-class explosive gases
Note: The absence of a temperature group indicator indicates that this instrument does not come into direct contact with explosive gases.
VI. Explosion Protection Terminology: Definition of Safety Barrier Parameters:
Maximum allowable voltage of the safety barrier: Um – The highest voltage that can be applied to the non-intrinsic safety side while ensuring the intrinsic safety performance of the intrinsic safety side of the safety barrier； Maximum open-circuit voltage of the safety barrier: Uoc, the maximum voltage when the intrinsically safe side is open within the maximum allowable voltage range ； Maximum short-circuit current of the safety barrier: Isc is the maximum current when the intrinsically safe side is short-circuited within the maximum allowable voltage range ； Safe barrier allowable distributed capacitance: Ca – the maximum allowable external capacitance at the intrinsically safe terminal while ensuring intrinsic safety ； Safety barrier allows distributed inductance: La represents the maximum allowable external inductance at the intrinsically safe side while ensuring intrinsically safe performance ； VII. Explanation of the format for explosion-proof markings: The explosive hazardous materials present in factories or mining areas are scientifically classified and graded based on their ignition energy, minimum ignition temperature, and the duration for which explosive gases are present at that location, in order to determine the appropriate explosion-proof markings and types of explosion-proof equipment needed. Explanation of 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 category: 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 there must be measures for fault self-detection; the safety factor in the event of a fault is 1.0.