Classification standards for explosion-proof ratings and the basic principles of explosion protection

2024-07-02 3796

The concept of explosion:

Explosion is the sudden transformation of a substance from one state to another through physical or chemical changes, releasing immense energy. The energy released at a rapid speed will cause violent impact and damage to surrounding objects. The three conditions that must be met for an explosion:

1）Explosive substances: substances that can react with oxygen (air), including gases, liquids, and solids. (Gas: hydrogen, acetylene, methane, etc.; Liquid: alcohol, gasoline; Solid: dust, fiber dust, etc.); ）Oxygen: Air. 3 ）Ignition sources: including open flames, electrical sparks, mechanical sparks, electrostatic sparks, high temperatures, chemical reactions, light energy, etc. Why explosion-proof:

Explosive substances; : Many production sites produce certain flammable substances. About two-thirds of the underground coal mines contain explosive substances; In the chemical industry, there are approximately; 80% The above production workshop areas contain explosive substances. Oxygen; : Oxygen in the air is ubiquitous. Ignite the source; In the production process, a large number of electrical instruments and various frictional electric sparks are used; , Mechanical wear sparks, electrostatic sparks, high temperatures, etc. are inevitable, especially when instruments and electrical components malfunction.

Objectively, many industrial sites meet explosive conditions. When the concentration of explosive substances mixed with oxygen is within the explosive limit range, if there is an explosion source, an explosion will occur. Therefore, it is necessary to adopt explosion-proof measures. The principle of instrument explosion-proof

Classification of Hazardous Areas:

Explosive substance

Regional definition

China; standard

North America; standard

Gas (Class I)

1. Under normal circumstances; , Explosive gas mixture continuous or long

The place where time exists

2. Under normal circumstances, explosive gas mixtures may occur

venue

Under normal circumstances, explosive gas mixtures are unlikely to occur,

Only under abnormal circumstances; , Occasional or short-lived places

0 district

1 district

2 district

Div.1

Div.2

Dust or fiber

(CLASS Ⅱ/

Ⅲ）

1. Under normal circumstances; , Explosive dust or combustible fibers and air

The mixture of gases may be continuous; , Places that frequently appear in a short period of time or exist for a long time

2. Under normal circumstances; , Explosive dust or combustible fibers and air

The mixture of gases cannot appear; , Only under abnormal circumstances; , Occasional or short-lived places

10 district

11 district

Div.1

Div.2

Applicability of explosion-proof methods to hazardous areas:

serial number	Explosion proof type	code name	National Standard	Explosion proof measures	Applicable Region
one	flameproof type	d	GB3836.2	Isolate existing ignition sources	Zone1,Zone2
two	increased safety	e	GB3836.3	Try to prevent the generation of ignition sources	Zone1,Zone2
three	intrinsically safe	ia	GB3836.4	Limit the energy of ignition sources	Zone0-2
four	intrinsically safe	ib	GB3836.4	Limit the energy of ignition sources	Zone1,Zone2
five	Positive pressure type	p	GB3836.5	Separate hazardous substances from ignition sources	Zone1,Zone2
six	Oil filled type	o	GB3836.6	Separate hazardous substances from ignition sources	Zone1,Zone2
seven	Sand filling mold	q	GB3836.7	Separate hazardous substances from ignition sources	Zone1,Zone2
eight	non-sparking	n	GB3836.8	Try to prevent the generation of ignition sources	Zone2
nine	exm	m	GB3836.9	Try to prevent the generation of ignition sources	Zone1,Zone2
ten	airtight	h	GB3836.10	Try to prevent the generation of ignition sources	Zone1,Zone2

Applicability of explosion prevention to hazardous areas:; Classification of Explosive Hazardous Gases

According to the potential spark energy, explosive gases are classified into four hazard levels in China, Europe, and most countries and regions around the world; , as shown in the table below; :

Working condition category	Gas classification	Representative gases	Ignite spark energy
Under the mine	I	methane	0.280mJ
Factories outside the mine	IIA	propane	0.180mJ
Factories outside the mine	IIB	ethylene	0.060mJ
Factories outside the mine	IIC	hydrogen	0.019mJ

The United States and Canada first divided explosive objects scattered in the air into three categories; CLASS (Class)

Don't): CLASS Gas and vapor; CLASS Ⅱ Dust CLASS Fiber III; . Then separate the gas and dust into; Group (Group); ):

Group Name	Representative gases or dust
A	acetylene

Explosion proof mark for instruments:

B	hydrogen
C	ethylene
D	propane
E	Metal dust
F	Coal dust
G	Grain dust

Classification of gas temperature groups:

Temperature; group	Safe objects; surface temperature	Common explosive gases
T1	≤ 450℃	Hydrogen, acrylonitrile, etc; 46 plant
T2	≤ 300℃ acetylene	Ethylene, etc; 47 plant
T3	≤ 200℃	Gasoline, butenal, etc; 36 plant
T4	≤ 135℃	Acetaldehyde, tetrafluoroethylene, etc; 6 plant
T5	≤ 100℃	carbon disulfide
T6	≤ 85℃	Ethyl nitrate and ethyl nitrite

Ex(ia)ⅡC T6 Meaning:

Logo content	symbol	meaning
Explosion proof declaration	Ex	Comply with certain explosion-proof standards, such as China's national standards
explosion-proof method	ia	Adopting ia Level of intrinsic safety explosion-proof method, can be installed in; Zone 0
gas category	ⅡC	Permitted to involve IIC; Explosive gas like substance
temperature group	T6	The surface temperature of the instrument shall not exceed; 85℃

Ex(ia)ⅡC Meaning:

Logo content

symbol

meaning

Classification standards for explosion-proof levels:

Explosion proof declaration	Ex	Compliant with European explosion-proof standards
explosion-proof method	ia	Adopting ia Level of intrinsic safety explosion-proof method, can be installed in; Zone 0
gas category	ⅡC	Permitted to involve IIC; Explosive gas like substance

Note : There is no temperature group item in this flag; , This instrument does not come into direct contact with explosive gases; . Explosion proof terminology:

Regarding explosion-proof terminology and standards; Definition of safety parameters for safety barriers:

Allowable voltage for safety barrier:; Um

Ensure the intrinsic safety performance of the safety barrier's intrinsic safety end and allow for the input of voltages that may not be present at the intrinsic safety end; Open circuit voltage of safety barrier:; Uoc

Voltage value when the intrinsic safety end is open circuit within the allowable voltage range; Short circuit current of safety barrier:; Isc

The current value when the intrinsic safety end is short circuited within the allowable voltage range; The safety barrier allows for distributed capacitance:; Ca

Under the condition of ensuring intrinsic safety performance, external capacitors are allowed to be connected to this safety end; The safety barrier allows for distributed inductance:; La

Under the condition of ensuring intrinsic safety performance, external inductance is allowed to be connected to the safety end of this device; Format description of explosion-proof signs:

Scientifically classify and grade the explosive hazardous media in factories or mining areas according to their ignition energy, ignition temperature, and the time period of the existence of explosive hazardous gases on site, in order to determine the explosion-proof signs and forms of on-site explosion-proof equipment.

Explosion proof mark format:

Ex (ia) ⅡC T4

Explosion proof mark Explosion proof grade Gas group Temperature group; Explosion proof grade description:

ia Level: Electrical equipment that cannot ignite explosive gas mixtures during normal operation, one fault, and two faults.

During normal operation, the safety factor is; 2.0 ；

When a fault occurs, the safety factor is; 1.5 ；

When there are two faults, the safety factor is; 1.0 。

Note: Contact points with sparks must be equipped with explosion-proof enclosures, airtight enclosures, or double the safety factor.

ib Level :

Electrical equipment that cannot ignite explosive gas mixtures during normal operation and a malfunction.

During normal operation, the safety factor is; 2.0 ；

When a fault occurs, the safety factor is; 1.5 。

During normal operation, contacts with sparks must be protected by explosion-proof or airtight enclosures, and there should be measures for fault self display. The safety factor in the event of a fault is ____; 1.0 。

◆ Explosion proof mark format:

Ex: Explosion proof mark (ia): Explosion proof grade Ⅱ C: Gas group T4: Temperature group

Explosion proof grade description: ia Level:

Electrical equipment that cannot ignite explosive gas mixtures due to one or two faults during normal operation. During normal operation, the safety factor is 2.0; When there is a malfunction, the safety factor is 1.5; During normal operation, contacts with sparks must be equipped with explosion-proof enclosures, airtight enclosures, or double the safety factor.

ib Level:

Electrical equipment that cannot ignite explosive gas mixtures during normal operation or during a malfunction. During normal operation, the safety factor is 2.0; When there is a malfunction, the safety factor is 1.5; During normal operation, contacts with sparks must be protected by explosion-proof or airtight enclosures, and measures for fault self display should be taken.

Explosive gas grouping comparison table:

Typical gas	Chinese Standard	North American standards	Ignition energy (micro coke)
propane	ⅡA	D	one hundred and eighty
ethylene	ⅡB	C	sixty
hydrogen	ⅡC	B	twenty
acetylene	ⅡC	A	twenty

Temperature group comparison table:

Surface temperature of electrical equipment (℃)	four hundred and fifty	three hundred	two hundred	one hundred and thirty-five	one hundred	eighty-five
temperature group	T1	T2	T3	T4	T5	T6

Electrical equipment type:

Class I	Electrical equipment used underground in coal mines
Class II	Factory electrical equipment

Explosion proof level: classified as A according to its safe clearance for explosive gas mixtures B C Level 3.

category	level	Experimental safety gap (MESG) mm
Ⅱ	A	0.9≤MESG
Ⅱ	B	0.5＜MESG＜0.9
Ⅱ	C	MESG≤0.5

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