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Explanation Of Explosion-Proof Signs

The explosion-proof marking in explosion-proof lighting fixtures is a label that describes the explosion-proof grade, temperature group, type, and applicable areas of the lighting fixture.

explosion proof level-1

Explanation of Explosion-proof Marking:

As per GB 3836 standards, the explosion-proof marking of lighting fixtures includes:

Explosion-proof Type + Equipment Category + (Gas Group) + Temperature Group.

1. Explosion-proof Type:

Table 1 Basic Types of Explosion-Proof

Explosion proof formExplosion proof form signExplosion proof formExplosion proof form sign
Flameproof typeEX dSand filled typeEX q
Increased safety typeEX eEncapsulationEX m
Barotropic typeEX pN-typeEX n
Intrinsically safe typeEX ia
EX i
Special typeEX s
Oil invasion typeEX oDust explosion-proof typeEX A
EX B

2. Equipment Category:

Electrical equipment for explosive gas atmospheres is divided into:

Class I: For use in coal mines;

Class II: For use in explosive gas atmospheres other than coal mines.

Class II explosion-proof “d” and intrinsic safety “i” electrical equipment are further divided into IIA, IIB, and IIC classes.

Electrical equipment for combustible dust environments is divided into:

Type A dust-tight equipment; Type B dust-tight equipment;

Type A dust-proof equipment; Type B dust-proof equipment.

3. Explanation of Explosion-proof Marking:

The ability of an explosive gas mixture to propagate an explosion indicates its level of explosion hazard. The greater the ability to propagate an explosion, the higher the danger. This ability can be represented by the maximum experimental safe gap. Additionally, the ease with which explosive gases, vapors, or mists can be ignited also indicates the level of explosion hazard, represented by the minimum igniting current ratio. Class II explosion-proof or intrinsic safety electrical equipment is further classified into IIA, IIB, and IIC based on their applicable maximum experimental safe gap or minimum igniting current ratio.
Table 2 Relationship between the Group of Explosive Gas Mixtures and the Maximum Experimental Safe Gap or Minimum Igniting Current Ratio

Gas groupMaximum test safety gap MESG (m m)Minimum ignition current ratio MICR
IIAMESG≥0.9MICR>0.8
IIB0.9>MESG≥0.50.8≥MICR≥0.45
IIC0.5≥MESG0.45>MICR

4. Temperature Group:

The ignition temperature of an explosive gas mixture is the limit temperature at which it can be ignited.
Electrical equipment is classified into T1 to T6 groups based on their highest surface temperature, ensuring that the maximum surface temperature of the equipment does not exceed the permissible value of the corresponding temperature group. The relationship between temperature groups, equipment surface temperature, and the ignition temperature of flammable gases or vapors is shown in Table 3.

Table 3 Relationship between Temperature Groups, Equipment Surface Temperature, and Ignition Temperature of Flammable Gases or Vapors

Temperature level IEC/EN/GB 3836The highest surface temperature of the equipment T [℃]Lgnition temperature of combustible substances [℃]
T1450T>450
T2300450≥T>300
T3200300≥T>200
T4135200≥T>135
T5100135≥T>100
T685100≥T>8

5. Requirements for Setting Markings:

(1) Markings should be prominently placed on the main body of the electrical equipment;
(2) The markings must remain clear and durable under potential chemical corrosion. Markings such as Ex, explosion-proof type, category, and temperature group can be embossed or debossed on the visible parts of the casing. The material for the marking plate should be chemically resistant, such as bronze, brass, or stainless steel.

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