Explosion Proof Grade: Do You Know the Classification Standard?

Why explosion proof?

Explosive substances: some combustible substances will be produced in many production sites.

About two-thirds of the underground coal mines have explosive substances;

Explosion Proof Grade: Do You Know the Classification Standard? 1

In the chemical industry, more than 80% of the production workshops have explosive substances.

Oxygen: oxygen in the air is ubiquitous.

Ignition source: a large number of electrical instruments are used in the production process.

Electric sparks of various friction, mechanical wear sparks, electrostatic sparks, high temperature, etc. are inevitable, especially when the instruments and electrical equipment fail.

Objectively, many industrial sites meet the explosion conditions.

When the mixed concentration of explosive substances and oxygen is within the explosion limit, explosion will occur if there is an explosion source.

Therefore, it is necessary to adopt explosion-proof measures.

Explosion Proof Grade: Do You Know the Classification Standard? 2

Hazard classification of hazardous places:

Explosive materials

Area Definition

Chinese standard

North American Standard

Gas(CLASSI)

Places where explosive gas mixtures exist continuously or for a long time under normal conditions.

Zone 0

 

Div.1

Places where explosive gas mixtures may occur under normal conditions.

Zone 1

 

Places where explosive gas mixtures are unlikely to occur under normal conditions, only occasionally or for a short time under abnormal conditions.

Zone 2

 

Div.2

Dust or fiber(CLASSII/III)

Under normal conditions, the explosive dust or the mixture of combustible fiber and air may occur continuously, frequently for a short time or exist for a long time.

Zone 10

 

Div.1

Under normal conditions, the explosive dust or the mixture of combustible fiber and air cannot appear, but only in abnormal conditions, occasionally or for a short time.

Zone 11

Div.2

Applicability of explosion protection to hazardous places:

NO.

Explosion proof type

 

 

code

national standard

Explosion proof measures

 

 

applicable scope

1

Flameproof type

 

 

d

GB3836.2

Isolate existing ignition sources

Zonel.Zone2

2

increased safety

e

GB3836.3

Try to prevent ignition source

Zone1.Zone2

3

Intrinsically safe

 

 

ia

GB3836.4

Limit the energy of the ignition source

Zone0-2

Intrinsically safe

 

 

ib

GB3836.4

Limit the energy of the ignition source

Zone1,Zone2

4

Barotropic type

p

GB3836.5

Hazardous substances shall be separated from ignition source

Zonel,Zone2

5

Oil filled type

o

GB3836.6

Hazardous substances shall be separated from ignition source

Zone1.Zone2

6

Sand filled mold

 

 

q

GB3836.7

Hazardous substances shall be separated from ignition source

Zone1.Zone2

7

Non sparking type

 

 

n

GB3836.8

Try to prevent ignition source

Zone2

8

exm

m

GB3836.9

Try to prevent ignition source

Zonel,Zone2

9

Airtight type

h

GB3836.10

Try to prevent ignition source

Zone1,Zone2

Classification of explosive dangerous gases

Explosion Proof Grade: Do You Know the Classification Standard? 3

According to the minimum spark energy that may be detonated, China, Europe and most countries and regions in the world classify explosive gases into four hazard levels, as shown in the following table:

Working condition category

Gas classification

Representative gas

Minimum ignition spark energy

Factory under the mine

I

Ifire-damp

0.280mJ

Factory outside the mine

 IA

propane

0.180mJ

IIB

ethylene

0.060mJ

IIC

hydrogen

0.019mJ

The United States and Canada first classified explosive objects dispersed in the air into three classes:

Class I gas and vapor;

Class Ⅱ dust;

Class III fiber.

Then the gas and dust are divided into groups:

GroupRepresentative gas or dust
Aethyne
Bhydrogen
Cethylene
Dpropane
Emetal dirt
Fcoal dust
Ggrain dust

Gas temperature group division:

Temperature groupsSafe object surface temperatureCommon explosive gas
T1≤450℃Hydrogen, acrylonitrile and other 46 kinds
T2≤300℃Acetylene, ethylene and other 47 kinds
T3≤200℃Gasoline, butenal and other 36kinds.
T4≤135℃Acetaldehyde, tetrafluoroethylene and other 6kind
T5≤100℃Carbon disulfide
T6≤85℃Ethyl nitrate and ethyl nitrite

Explosion proof signs of instruments

Meaning of Ex (ia) Ⅱ C T6:

Sign content:SymbolMeaning
Explosion proof declarationExComply with certain explosion-proof standards, such as China’s national standards
Explosion proof modeiaClass ia intrinsically safe explosion-proof method is adopted, which can be installed in Zone 0
Gas category:IICIt is allowed to involve class IIC explosive gas
Temperature groupsT6The instrument surface temperature shall not exceed 85 ℃

Meaning of Ex (ia) Ⅱ C:

Sign content:SymbolMeaning
Explosion proof declarationExComply with European explosion-proof standards
Explosion proof modeiaClass ia intrinsically safe explosion-proof method is adopted, which can be installed in Zone 0.
Gas category:IICIt is allowed to involve class IIC explosive gas.

Note: there is no temperature group item in this sign, indicating that the instrument is not in direct contact with explosive gas.

Explosion proof terminology:

Definition of safety parameters of safety barrier:

  • Maximum allowable voltage of safety barrier: Um

Ensure the intrinsic safety performance of the intrinsically safe end of the safety barrier, and allow the maximum voltage that may be input by the non intrinsically safe end.

  • Maximum open circuit voltage of safety barrier: Uoc.

The maximum voltage when the intrinsically safe terminal is open within the maximum allowable voltage range.

  • Maximum short circuit current of safety barrier: Isc.

Maximum value of current when the intrinsically safe terminal is short circuited within the maximum allowable voltage range.

  • Allowable distributed capacitance of safety barrier: Ca

The maximum allowable external capacitance of the intrinsically safe terminal under the condition of ensuring the intrinsic safety performance.

  • Allowable distributed inductance of safety barrier: La

The maximum allowable external inductance of the intrinsically safe terminal under the condition of ensuring the intrinsic safety performance.

Format description of explosion-proof sign:

The explosive hazardous medium in the factory or mining area shall be scientifically classified and graded according to its ignition energy, minimum ignition temperature and time period of existence of explosive hazardous gas on site, so as to determine the explosion-proof signs and forms of explosion-proof equipment on site.

Format of explosion-proof sign:

Ex (ia) ⅡC T4

Explosion proof mark explosion-proof grade gas group temperature group

Explosion Proof Grade: Do You Know the Classification Standard? 4

Explosion proof grade description:

Grade ia:

Electrical equipment that cannot ignite explosive gas mixture under normal operation with one fault and two faults.

During normal operation, the safety factor is 2.0;

In case of one fault, the safety factor is 1.5;

In case of two faults, the safety factor is 1.0.

Note: the contact with spark must be provided with explosion-proof shell, air tight shell or double the safety factor.

Grade ib:

Electrical equipment that cannot ignite explosive gas mixture during normal operation with one failure.

During normal operation, the safety factor is 2.0;

In case of one fault, the safety factor is 1.5.

During normal operation, the contact with spark shall be protected by flameproof enclosure or airtight enclosure, and measures for fault self display shall be taken.

The safety factor of one fault is 1.0.

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