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Explosion-Proof Level Analysis

Let’s start by explaining the various explosion-proof ratings, what they signify, and how to choose them in practice, using explosion-proof distribution boxes as an example.

Gas group/temperature groupT1T2T3T4T5T6
IIAFormaldehyde, toluene, methyl ester, acetylene, propane, acetone, acrylic acid, benzene, styrene, carbon monoxide, ethyl acetate, acetic acid, chlorobenzene, methyl acetate, chlorineMethanol, ethanol, ethylbenzene, propanol, propylene, butanol, butyl acetate, amyl acetate, cyclopentanePentane, pentanol, hexane, ethanol, heptane, octane, cyclohexanol, turpentine, naphtha, petroleum (including gasoline), fuel oil, pentanol tetrachlorideAcetaldehyde, trimethylamineEthyl nitrite
IIBPropylene ester, dimethyl etherButadiene, epoxy propane, ethyleneDimethyl ether, acrolein, hydrogen carbide
IICHydrogen, water gasAcetyleneCarbon disulfideEthyl nitrate

Certification marking:

Ex d IIB T4 Gb/Ex tD A21 IP65 T130°C is a universal certificate for gas and dust explosion protection, where the part before the slash (/) indicates the gas explosion-proof level, and the part after the slash indicates dust explosion-proof.

Ex: Explosion-proof marking, the standard format of IEC (International Electrotechnical Commission) explosion-proof ratings.

d: Flameproof type, indicating the primary form of explosion protection is flameproof.

IIB: Represents Class B gas explosion protection.

T4: Indicates the temperature class.

Gb: Indicates this product is suitable for Zone 1 explosion protection.

For the dust explosion part in the latter half, it’s sufficient to achieve the highest dust protection grade 6 based on the gas explosion-proof standards.

tD: Represents the type of enclosure protection (preventing dust ignition with enclosure).

A21: Indicates the applicable area, suitable for Zone 21, Zone 22.

IP65: Represents the protection grade.

It’s crucial to choose the correct explosion-proof rating in actual environments.

First, it’s important to understand two main categories, as described below:

Explosion-proof types:

Class I: Electrical equipment for underground coal mines;

Class II: Electrical equipment for all other explosive gas environments except coal mines and underground.

Class II can be divided into IIA, IIB, and IIC, where equipment marked IIB can be used under conditions suitable for IIA devices; IIC can be used under conditions suitable for both IIA and IIB.

Class III: Electrical equipment for explosive dust environments other than coal mines.

IIIA: Combustible flyings; IIIB: Non-conductive dust; IIIC: Conductive dust.

Explosion-proof areas:

Zone 0: Where explosive gases are always or frequently present; continuously hazardous for more than 1000 hours/year;

Zone 1: Where flammable gases might occur during normal operation; intermittently hazardous for 10 to 1000 hours/year;

Zone 2: Where flammable gases are not normally present and, if they occur, are likely to be infrequent and short-lived; hazardously present for 0.1 to 10 hours/year.

It is important to note that we deal with Class II and III, Zone 1, Zone 2; Zone 21, Zone 22.

Typically, reaching IIB is sufficient for gases, but for hydrogen, acetylene, and carbon disulfide, a higher level of IIC is required. For dust explosion protection, just achieve the corresponding gas explosion-proof level and the highest dust grade.

There’s also a combined type of explosion-proof distribution box rating: ExdeIIBT4Gb.

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