Explosion Proof Grade: Do You Know the Classification Standard?

Why explosion proof?

Explosive Substances: Some flammable substances are produced in numerous production sites. Approximately two-thirds of underground coal mines contain explosive substances.

In the chemical industry, over 80% of the production facilities contain explosive substances.

Oxygen is present throughout the air. There are numerous electrical instruments utilized in the production process, which can serve as an ignition source. Electrical sparks from friction, mechanical wear, electrostatic discharge, high temperature, etc. are common and especially likely to occur when instruments and electrical equipment malfunction.

Many industrial sites objectively meet the conditions for an explosion. When the mixture of explosive substances and oxygen is within the explosive limit, an explosion will occur if there is an ignition source. Thus, it is crucial to implement explosion-proof measures.

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

According to the minimum energy required to ignite an explosive gas, China, Europe, and most countries around the world classify explosive gases into four hazard levels based on 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 initially categorized explosive objects dispersed in the air into three categories:

Class I: Gases and vapors;

Class II: Dusts;

Class III: Fibers.

Then, the gases and dusts were further 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: This symbol does not include a temperature group, indicating that the instrument is not in direct contact with the explosive gas.

Explosion proof terminology:

Definitions of Safety Barrier Parameters:

Maximum Allowable Voltage of Safety Barrier: Um This parameter ensures the intrinsic safety performance of the intrinsically safe end of the safety barrier, and it represents the maximum voltage that may be input at the non-intrinsically safe end.

Maximum Open Circuit Voltage of Safety Barrier: Uoc This parameter represents the maximum voltage when the intrinsically safe terminal is open within the maximum allowable voltage range.

Maximum Short Circuit Current of Safety Barrier: Isc This parameter represents the maximum current value when the intrinsically safe terminal is short-circuited within the maximum allowable voltage range.

Allowable Distributed Capacitance of Safety Barrier: Ca This parameter represents the maximum allowable external capacitance of the intrinsically safe terminal while ensuring intrinsic safety performance.

Allowable Distributed Inductance of Safety Barrier: La This parameter represents the maximum allowable external inductance of the intrinsically safe terminal while ensuring intrinsic safety performance.

Format Description of Explosion-Proof Sign:

The explosive hazardous substances in the factory or mining area must be scientifically categorized and graded based on their ignition energy, minimum ignition temperature, and the duration of the presence of explosive hazardous gas on the site. This information is used to determine the explosion-proof signs and the explosion-proof equipment required on the site.

Format of Explosion-Proof Sign:

Ex (ia) ⅡC T4

This format consists of the explosion-proof mark, explosion-proof grade, gas group, and temperature group.

Explosion proof grade description:

Grade ia:

Electrical equipment that cannot ignite explosive gas mixtures during normal operation, even with one fault or two faults.

During normal operation, the safety factor is 2.0; in the event of one fault, the safety factor is 1.5; and in the case of two faults, the safety factor is 1.0.

Note: Any contact with sparks must be equipped with an explosion-proof casing, airtight casing, or a double safety factor.

Grade ib:

Electrical equipment that is unable to ignite explosive gas mixtures even in the event of one failure during normal operation.

The safety factor during normal operation is 2.0, and in the event of one fault, the safety factor is 1.5.

During normal operation, contact with sparks must be protected by a flameproof enclosure or airtight enclosure, and measures for fault self-diagnosis must be implemented.

The safety factor in case of one fault is 1.0.

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Shane
Author

Shane

Founder of MachineMFG

As the founder of MachineMFG, I have dedicated over a decade of my career to the metalworking industry. My extensive experience has allowed me to become an expert in the fields of sheet metal fabrication, machining, mechanical engineering, and machine tools for metals. I am constantly thinking, reading, and writing about these subjects, constantly striving to stay at the forefront of my field. Let my knowledge and expertise be an asset to your business.

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