Classification of Electrical Equipment for Explosive Atmospheres

Class I: Class I electrical equipment is used in coal mine gas environments.

Class II: Class II electrical equipment is used in explosive gas atmospheres other than coal mine methane gas; Class II electrical equipment can be further divided into IIA, IIB, and IIC classes according to the type of explosive atmosphere intended.

Class III: Class III electrical equipment is used in explosive dust atmospheres other than coal mines; Class III electrical equipment can be further divided into IIIA, IIIB, and IIIC classes according to the characteristics of the explosive dust atmosphere intended.

Classification of Hazardous Locations

Explosive Gas Atmosphere	Zone 0	Locations where explosive gas atmospheres are present continuously or for long periods.
	Zone 1	Locations where explosive gas atmospheres are likely to occur during normal operation.
	Zone 2	Locations where explosive gas atmospheres are not likely to occur during normal operation, and if they do, it is only occasionally and for a short period.
Combustible Dust Atmosphere	Zone 20	Locations and internal parts of containers where combustible dust is present continuously or frequently in quantities sufficient to form combustible dust-air mixtures and/or may form uncontrollable and thick dust layers during normal operation.
	Zone 21	Locations where combustible dust in quantities sufficient to form combustible dust-air mixtures may occur during normal operation but are not classified as Zone 20; this includes areas directly adjacent to dust charging or discharging points, locations where dust layers appear, and places where combustible dust-air mixtures may form under normal operation.
	Zone 22	Locations where combustible dust clouds occasionally appear under abnormal conditions and only for short periods, or where combustible dust occasionally accumulates or dust layers may exist and combustible dust-air mixtures may form. If it is not possible to ensure the exclusion of combustible dust accumulation or dust layers, the area should be classified as Zone 21.

Classification Method for Gases and Vapors

◆ According to national standard GB/T3836.1, Class II explosion-proof type "d" and intrinsically safe type "i" electrical equipment are further divided into IIA, IIB, and IIC classes.

◆ For explosion-proof electrical equipment, the classification of gases and vapors is based on the Maximum Experimental Safe Gap (MESG). The limit values are:

Class A: MESG greater than 0.9mm

Class B: MESG 0.5mm to 0.9mm

Class C: MESG less than 0.5mm

◆ For intrinsically safe electrical equipment, the classification of gases and vapors is based on the ratio of their Minimum Ignition Current (MIC) to the MIC of laboratory methane.

The limit values are:

Class A: MIC ratio greater than 0.8

Class B: MIC ratio 0.45 to 0.8

Class C: MIC ratio less than 0.45

Note: Equipment marked IIB can also be used under conditions for IIA equipment; equipment marked IIC can also be used under conditions for IIA and IIB equipment.

Maximum Surface Temperature Classification of Class II Electrical Equipment

Temperature Difference Group	Maximum Surface Temperature (℃)
T1	450
T2	300
T3	200
T4	135
T5	100
T6	85

Gas and Vapor Classes and Temperature Groups

Name of Gas or Vapor	Class	Temperature Group	Name of Gas or Vapor	Class	Temperature Group
Methane	IIA	T1	Ethanol	IIA	T2
Ethane	IIA	T1	Propanol	IIA	T2
Propane	IIA	T2	Butanol	IIA	T2
Butane	IIA	T3	Pentanol	IIA	T3
Pentane	IIA	T3	Hexanol	IIA	T3
Hexane	IIA	T3	Heptanol	IIA	-
Heptane	IIA	T3	Octanol	IIA	-
Octane	IIA	T3	Nonanol	IIA	-
Nonane	IIA	T3	Cycloethanol	IIA	T3
Decane	IIA	-	Methylcyclohexanol	IIA	T3
Cyclobutane	IIA	T2	Phenol	IIA	T1
Cyclopentane	IIA	T3	Cresol	IIA	T1
Cyclohexane	IIA	-	4-Hydroxy-4-methylpentanone (Diacetone alcohol)	IIA	T1
Cycloheptane	IIA	-	Acetaldehyde	IIA	T4
Methylcyclobutane	IIA	T2	Polyacetaldehyde	IIA	-
Methylcyclopentane	IIA	T3	Acetone	IIA	T1
Methylcyclohexane	IIA	T3	Methyl ethyl ketone (Butanone)	IIA	T1
Ethylcyclobutane	IIA	T3	Pent-2-one (Methyl propyl ketone)	IIA	T1
Ethylcyclopentane	IIA	T3	Hex-2-one (Methyl butyl ketone)	IIA	T1
Ethylcyclohexane	IIA	T3	Pentyl methyl ketone	IIA	-
Decahydronaphthalene (Naphthene)	IIA	T2	Pent-2,4-dione (Pentane-2,4-dione)	IIA	T2
Propylene	IIA	T1	Cyclohexanone	IIA	T2
Styrene	IIA	T1	Methyl formate	IIA	T2
Methyl styrene	IIA	T1	Ethyl formate	IIA	T2
Benzene	IIA	T1	Methyl acetate	IIA	T1
Toluene	IIA	T1	Ethyl acetate	IIA	T2
Xylene	IIA	T2	Propyl acetate	IIA	T2
Ethylbenzene	IIA	T1	Acetate ester	IIA	T2
Trimethylbenzene	IIA	T1	Pentyl acetate	IIA	T2
Naphthalene	IIA	T2	Methyl methacrylate	IIA	T2
Isopropylbenzene	IIA	T2	Ethyl methacrylate	IIA	-
Methyl isopropylbenzene	IIA	T1	Vinyl acetate	IIA	T2
Methane (Industrial)	IIA	T3	Ethyl acetoacetate	IIA	T2
Turpentine	IIA	T3	Acetic acid	IIA	T1
Naphtha	IIA	T3	Chloromethane	IIA	T1
Coal tar naphtha	IIA	T3	Chloroethane	IIA	T1
Petroleum (including gasoline)	IIA	T3	Bromoethane	IIA	T1
Solvent naphtha or cleaning naphtha	IIA	T3	1-Chloropropane	IIA	T1
Fuel oil	IIA	T3	Chlorobutane	IIA	T3
Kerosene	IIA	T3	Bromobutane	IIA	T3
Diesel	IIA	T3	Ethylene oxide	IIA	T2
Power benzene	IIA	T1	Propylene oxide	IIA	T1
Carbon monoxide	IIA	T1	Chlorobenzene	IIA	T1
Dipropyl ether	IIA	-	Benzyl chloride	IIA	T1
Methanol	IIA	T2	Dioxobenzene	IIB	T1
Allyl chloride	IIA	T2	Propyne (Methyl acetylene)	IIB	T1
Ethylene oxide	IIA	T1	Ethylene	IIB	T2
Vinyl chloride	IIA	T2	Cyclopropylene	IIB	T1
DDD-trifluorotoluene	IIA	T1	1,3-Butadiene	IIB	T2
Dimethylene oxide	IIA	T1	Acrylonitrile	IIB	T1
Acetyl chloride	IIA	T3	Isopropyl nitrate	IIB	-
Chloroethanol	IIA	T2	Hydrogen cyanide	IIB	T1
Ethyl mercaptan	IIA	T3	Dimethyl wall	IIB	T3
1-Propanethiol	IIA	-	Ethyl methyl ketone	IIB	T4
Thiophene	IIA	T2	Diethyl ether	IIB	T4
Tetrahydrothiophene	IIA	T3	Dibutyl	IIB	T4
Ammonia	IIA	T1	Ethylene oxide	IIB	T2
Cyanomethane	IIA	T1	12-Epoxypropane	IIB	T2
Ethyl nitrite	IIA	T6	1,3-Dioxolane	IIB	-
Nitromethane	IIA	T2	1,4-Dioxane	IIB	T2
Nitroethane	IIA	T2	1,3,5-Trioxane	IIB	T2
Methylamine	IIA	T2	Hydroxyethyl acetate	IIB	-
Dimethylamine	IIA	T2	Chloromethylfurfural	IIB	T3
Trimethylamine	IIA	T4	Methyl acrylate	IIB	T2
Diethylamine	IIA	T2	Ethyl acrylate	IIB	T2
Triethylamine	IIA	T1	Furan	IIB	T2
n-Propylamine	IIA	T2	Butenal	IIB	T3
n-Butylamine	IIA	T2	Acrolein	IIB	T3
Cycloethylamine	IIA	T3	Tetrahydrofuran	IIB	T3
2-Aminoethanol (Ethanolamine)	IIA	-	Coke oven gas	IIB	T1
2-Diaminoethanol	IIA	-	Tetrafluoroethylene	IIB	T4
Diethylaminoethanol	IIA	T2	1-Chloro-2,3-epoxypropane	IIB	T2
Aniline	IIA	T1	Ethyl mercaptan	IIB	T3
N,N-Dimethylaniline	IIA	T2	Carbon disulfide	IIB	T2
Phenylamino propanol	IIA	-	Hydrogen	IIC	T1
Toluidine	IIA	T1	Acetylene	IIC	T2
Azabenzene (Pyridine)	IIA	T1	Carbon disulfide	IIC	T5

Correspondence between gas temperature group and equipment temperature group

Gas temperature group	Gas natural temperature (T)	Equipment temperature group
		T6 (85℃)	T5 (100℃)	T4 (135℃)	T3 (200℃)	T2 (300℃)	T1 (450℃)
T6	85℃ ≤ T ≤ 100℃	○	●	●	●	●	●
T5	100℃ < T ≤ 135℃	○	○	●	●	●	●
T4	135℃ < T ≤ 200℃	○	○	○	○	●	●
T3	200℃ < T ≤ 300℃	○	○	○	○	○	●
T2	300℃ < T ≤ 450℃	○	○	○	○	○	○
T1	450℃ < T	○	○	○	○	○	○

● Explosion hazard ○ Equipment can be safely used

Explosion-proof mark explanation example

Symbol breakdown	Chinese explanation
Ex	Explosion-proof mark
db	Main protection measure: Flameproof type
eb	Auxiliary protection measure: Increased safety type
II	Equipment category: Explosive gas atmospheres except coal mines
C	Gas group
T6	Temperature group (maximum surface temperature ≤ 85℃)
Gb	Equipment protection level
Ex	Explosion-proof mark
tb	Explosion-proof type: Enclosure protection type (Class IIIA equipment)
III	Equipment category: For explosive dust atmospheres
C	Dust category: Conductive dust
T80℃	Maximum surface temperature < 80℃
Db	Equipment protection level

Current effective national standards

GB/T 3836.1-2021 Explosive atmospheres Part 1: Equipment General requirements

GB/T 3836.2-2021 Explosive atmospheres Part 2: Equipment protected by flameproof enclosure "d"

GB/T 3836.3-2021 Explosive atmospheres Part 3: Equipment protected by increased safety "e"

GB/T 3836.4-2021 Explosive atmospheres Part 4: Equipment protected by intrinsic safety "i"

GB/T 3836.5-2021 Electrical equipment for explosive gas atmospheres Part 5: Pressurized enclosure type "p"

GB/T 3836.6-2017 Electrical equipment for explosive gas atmospheres Part 6: Oil-immersed type "o"

GB/T 3836.7-2017 Electrical equipment for explosive gas atmospheres Part 7: Sand-filled type "q"

GB/T 3836.8-2021 Explosive atmospheres Part 8: Equipment protected by type "n"

GB/T 3836.9-2021 Explosive atmospheres Part 9: Equipment protected by encapsulation type "m"

GB/T 3836.11-2022 Explosive atmospheres Part 11: Test methods and data for classification of gases and vapors

GB/T 3836.12-2019 Explosive Atmospheres Part 12: Test Methods for Characteristics of Combustible Dusts

GB/T 3836.13-2021 Explosive Atmospheres Part 13: Repair, Overhaul, Restoration and Modification of Equipment

GB 3836.14-2014 Explosive Atmospheres Part 14: Classification of Locations Explosive Gas Atmospheres

GB/T 3836.15-2017 Explosive Atmospheres Part 15: Design, Selection and Installation of Electrical Equipment

GB/T 3836.16-2022 Explosive Atmospheres Part 16: Inspection and Maintenance of Electrical Equipment

GB/T 3836.31-2021 Explosive Atmospheres Part 31: Equipment Protected by Dust Ignition-Proof Enclosure "t"

Note: 1. Due to revisions and updates of national standards, the validity of the above standards may change. For details, please visit the website of the National Standardization Administration Committee;

2. The above national standards are all mandatory standards and can be downloaded for free from the "Mandatory National Standards Free Reading System" (http://www.gb168.cn/foc/).

Explosion-proof Type

Protection Method	Marking	Legend	Explosion-proof Principle	Applicable Area	Standard Number
Flameproof Type	d		Place parts of the equipment that may generate sparks or arcs during normal operation inside a flameproof enclosure. The flameproof enclosure can withstand the pressure of internal explosion without damage, and can ensure that flames and heat generated during internal explosion are extinguished and cooled at the flameproof joint, so as not to ignite explosive gases outside the enclosure. GB/T 3836.2	Zone 1 Zone 2	Increased Safety Type
e	No arcs, sparks or dangerous high temperatures are generated during normal operation, and further protective measures are taken structurally to improve the safety and		reliability of the equipment. GB/T 3836.3 Intrinsic Safety Type	Zone 1 Zone 2	i
The internal circuits of the equipment under specified conditions, whether in normal operation or specified fault conditions, do not produce electric sparks or thermal effects that can ignite explosive gases. GB/T 3836.4	Pressurized Enclosure Type		p Maintain the pressure of the internal protective gas higher than the surrounding atmospheric pressure to prevent explosive gases from entering the enclosure, or allow sufficient protective gas to flow through the enclosure, reducing the concentration of explosive gases inside to below the lower explosive limit.	Zone 0 Zone 1 Zone 2	GB/T 3836.5
Oil Immersion Type O	Immerse the components of electrical equipment entirely in protective liquid so that the equipment cannot ignite explosive gases on the liquid surface or outside the enclosure.		GB/T 3836.6 Sand Filled Type q	Zone 1 Zone 2	Completely embed conductive parts that can ignite explosive gases in filling material to prevent ignition of external explosive gases.
GB/T 3836.7	"n" Type		n Electrical equipment cannot ignite surrounding explosive gases (under normal operating conditions and uncertain abnormal operating conditions).	Zone 1 Zone 2	GB/T 3836.8
Encapsulation Type	m		Encapsulate parts that may ignite explosive gases in a compound so that they cannot ignite surrounding explosive gases. GB/T 3836.9	Zone 1 Zone 2	Selection, Installation and Maintenance of Explosion-proof Electrical Equipment
◆ Determine hazardous area classification based on the release of combustible substances and ventilation conditions on site;	◆ Determine the level and temperature group of electrical equipment based on the characteristics of gases and vapors;		◆ Select explosion-proof electrical equipment that meets the hazardous area classification and gas level temperature group according to the function used; ◆ After receipt, check the nameplate technical parameters, spare parts and installation accessories according to the packing list;	Zone 2	◆ Choose steel conduit wiring or cable wiring according to the product structure characteristics;
◆ Select rubber-sheathed cables suitable for the size of the sealing ring;	◆ Ensure that the sealing rings and gaskets inside the entry device are installed in the correct order;		◆ Ensure that the pressing elements (compression nuts or steel pipes) firmly press the sealing rings and reliably clamp the cables; Cannot ignite explosive gases around.	Zone 1 Zone 2	GB/T 3836.9

Selection, installation, and maintenance of explosion-proof electrical equipment

◆ Determine the classification of hazardous areas based on the release of flammable substances and ventilation conditions on site;

◆ Determine the level and temperature group of electrical equipment based on the characteristics of gases and vapors;

◆ Select explosion-proof electrical equipment that meets the temperature group requirements for hazardous location classification and gas level based on its usage function;

◆ After receiving the goods, check the technical parameters of the nameplate, spare parts, and installation accessories according to the packing list;

◆ Choose steel pipe wiring or cable wiring based on the structural characteristics of the product;

◆ Select rubber sheathed cables suitable for sealing ring size;

◆ Ensure that the sealing rings and gaskets inside the introduction device are installed correctly in sequence;

◆ Ensure that the clamping element (clamping nut or steel pipe) firmly compresses the sealing ring and securely clamps the cable;

◆ Reliably seal unused extra entry ports on the equipment with steel blocking plates;

◆ Reliably connect the internal and external grounding of electrical equipment to the on-site grounding system;

◆ Securely press the power cables into the terminal blocks;

◆ Regularly inspect the sealing rings inside the entry devices and the rubber components on the electrical equipment for signs of aging;

◆ Regularly inspect the explosion-proof joint surfaces of explosion-proof products and apply anti-rust oil;

◆ Regularly check the terminal blocks and internal and external grounding for any looseness;

◆ Keep the equipment appearance clean and intact.