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Explosion protection (explosion protection) refers to the ability to resist the impact of the explosion and heat without loss of normal operation is called explosion protection, to prevent the generation of explosions must be considered from the three necessary conditions, limiting one of the necessary conditions to limit the generation of explosions.

Three necessary conditions

1, the three conditions necessary to cause an explosion, three conditions at the same time — explosion

ignite ignite; combustion gases comburant (special substances can be non-O conditions of combustion and explosion, such as Mg in carbon dioxide can burn violently); combustible combustible.

2, to prevent the emergence of explosions must be considered from the three necessary conditions, to limit one of the necessary conditions, to limit the emergence of explosions.

prevent chemical plants, refineries in the explosive and flammable substances may cause an explosion.

Equipment and piping due to poor sealing caused by the escape of explosive or flammable substances, encountered in the instrumentation of the electrical contacts and electrical equipment short-circuit sparks formed, may cause an explosion or combustion.

Explosion proof measures

(1) Select the appropriate Explosion proof instrumentation and Explosion proof electrical equipment, the standard structure: Explosion proof, increased safety, positive pressure, sand-filled, intrinsically safe and oil-filled.

(2) Selection of adapted ventilation methods.

(3) Prevent or minimize the possibility of leakage of flammable substances.

(4) Do not use or minimize the use of electrical components that are prone to sparks.

(5) Maintain an inert state by filling with nitrogen gas.

Explosion proof design

In the building design, should be reasonable to determine the requirements of the building:

(1) the number of floors of the building. Generally appropriate to use a single-story building. For must take the bottom-up or top-down production process flow of the building can be used only multi-story building.

In the multi-storey building, if only part of the Explosion proof room, it should be arranged as far as possible in the uppermost floor, can not be arranged in the basement or semi-basement.

If the Explosion proof process is up and down until the top of the top floor, should be opened on each floor relief holes, the area should not be less than 15% of the floor area, the roof of the lightweight pressure relief roof.

② fire resistance level. Explosions often lead to fire, Explosion proof buildings should have a high fire resistance rating: single-story building not less than two, multi-story building should be a level.

③ structure type. In order to avoid the explosion caused by the collapse of the building, the building should be selected explosion-resistant load-bearing structure, and take pressure relief measures. Generally reinforced concrete structure; if the wall is thicker or Explosion proof building area is very small, can be used to brick wall load-bearing mixed structure, but must set up a lightweight pressure relief roof.

④ plane shape. The building plane should be rectangular. The smaller the width of the building, the larger the ratio of external wall area to volume, the more conducive to light, ventilation and pressure relief. The width of multi-storey building should not be more than 18 meters.

⑤ Safety entrances and exits. Safety evacuation entrances and exits, generally should not be less than two, and must meet the safety evacuation distance and evacuation width and other requirements.

⑥ Explosion proof section layout. Buildings only need to be partially Explosion proof, the Explosion proof section should be arranged by the external wall, requiring at least two external wall surfaces;

If there is only one external wall surface, its area should account for more than 25% of the total perimeter of the room. production of explosives in the plant, it is appropriate to use open or semi-open building.

Explosion proof equipment

Definition: electrical equipment that will not cause ignition of the surrounding explosive environment under specified conditions.

Divided into three categories:

Class Ⅰ: coal mine underground electrical equipment;

Class Ⅱ: in addition to coal mines, underground, all other electrical equipment for explosive atmospheres.

Class Ⅱ can be divided into Ⅱ A, Ⅱ B, Ⅱ C class, mark Ⅱ B equipment can be applied to Ⅱ A equipment conditions of use; Ⅱ C can be applied to Ⅱ A, Ⅱ B conditions of use.

Class III: electrical equipment used in explosive dust environments other than coal mines

Class III electrical electrical equipment in divided into: Class IIIA: combustible flotsam; Class IIIB: non-conductive dust; Class IIIC: conductive dust.

Note: Ⅱ C mark is a higher level of Explosion proof, but does not mean that the equipment has the best performance.

Maximum surface temperature: electrical equipment in the specified range of the most unfavorable operating conditions, may cause the surrounding explosive environment ignition of any part of the electrical equipment to reach the highest temperature. The maximum surface temperature should be lower than the combustible temperature.

For example: Explosion proof sensor environment of the explosive gas ignition temperature of 100 ℃, then the sensor in the most adverse operating conditions, the maximum surface temperature of any of its components should be less than 100 ℃.

Temperature group: electrical equipment for explosive atmospheres according to its maximum surface temperature is divided into T1-T6 groups

T1	T2	T3	T4	T5	T6
450 ℃	300 ℃	200℃	135 ℃	100 ℃	85℃

Explosion proof way

Explosive hazardous media in factories or mining areas, according to its ignition energy, minimum ignition temperature and the presence of explosive hazardous gases on-site time period for scientific classification and grading, in order to determine the Explosion proof equipment on-site Explosion proof signs and Explosion proof form.

Explanation of terms:

ia class: in normal operation, a fault and two faults can not ignite the explosive gas mixture of electrical equipment.

For normal operation, the safety factor is 2.0; for one fault, the safety factor is 1.5; for two faults, the safety factor is 1.0.

Note: Contacts with sparks must be added with Explosion proof enclosure, gas-tight enclosure or doubled to increase the safety factor.

Class ib: Electrical equipment that cannot ignite explosive gas mixtures during normal operation and one fault.

In normal operation, the safety factor is 2.0; in case of a fault, the safety factor is 1.5.

In normal operation, the spark contacts shall be protected by Explosion proof or gas-tight enclosure, and there are measures for self-display of faults, and the safety coefficient is 1.0 for one fault.

EExd: means the meaning of the explosion package;

IIC: refers to the ignition energy uJ,280,>180,60…. .80,<60; T6: means the temperature group, that is, electrical equipment according to its maximum surface temperature is divided into different temperature groups. The temperature groups of gases are divided according to different ignition temperatures. t6 is 85 degrees.

Explosion proof electrical equipment (d): refers to the components that can ignite the explosive mixture is enclosed in a shell, the shell can withstand the explosion pressure of the internal explosive mixture and prevent and the surrounding explosive mixture and the explosive mixture of electrical equipment.

Increased safety electrical equipment (e): under normal operating conditions, does not produce ignition of explosive mixtures of sparks or dangerous temperatures, and in the structure of measures to improve the degree of safety, in order to avoid the phenomenon of ignition in the normal and specified overload conditions of electrical equipment.

Intrinsically safe electrical equipment (i): Electrical equipment in which neither sparks nor thermal effects can ignite explosive mixtures under normal operation or under standard test conditions.

Non-sparking electrical equipment (n): in normal operating conditions do not produce arcs or sparks, and does not produce can ignite the surrounding explosive mixture of high-temperature surfaces or scorching points, and generally does not occur with the ignition of the failure of the electrical equipment.

Explosion proof special type (s): electrical equipment or components using GB3836-83 not included in the Explosion proof type, the competent authorities to develop temporary regulations. Sent to the Ministry of Labor and Personnel for the record, and by the designated identification unit test, according to the special electrical equipment “s” type disposal.

Explosive area

Hazardous areas of the meaning of the region is the actual existence of the possibility of hazardous measurements, which provides for the applicable Explosion proof type.

1, the International Electrotechnical Commission / European Electrotechnical Commission classified hazardous areas class classification:

Zone 0 (Zone 0): Explosive gases always or for a long time; continuous presence of hazardous greater than 1000 hours / year area;

Zone 1 (Zone 1): flammable gases are likely to occur or exist during the proper operation of the instrument; intermittent presence of hazardous 10~1000 hours/year;

Zone 2: In general, there is no flammable gas and even if it occurs occasionally, the base time of existence is very short; the danger of accidental state exists in the area of 0.1~10 hours/year;

China is divided into hazardous areas and the same as above.

2, explosive area classification, international standards and U.S. standards for comparison

I.E.C.

Gas Zone 0, Zone 1, Zone 2

Dust Zone 20, Zone 21, Zone 22

N.E.C.

Gases Class I, Division I, Class I, Division I, Class I, Division II

Dust Class II, Division I, Class II, Division II

I.E.C.: Internaional Electrotechnical Commission

N.E.C.: National Electrical Code, U.S.A.

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