1. Hazardous environment

Different types of explosion-proof electrical equipment shall be selected for different hazardous environments, and different explosion-proof measures shall be taken. Therefore, first of all, the size and level of the environmental hazardous area must be correctly divided.

According to the frequency and duration of explosive gas mixture, such hazardous environment is divided into zone 0, zone 1 and zone 2. The size of hazardous areas is affected by ventilation conditions, characteristics of release sources and performance parameters of hazardous substances.

How to select correct explosion-proof electrical equipment

① Zone 0 (Class 0 Hazardous Area) refers to the area where explosive gas, vapor or mist occurs continuously or for a long time or frequently in a short time during normal operation. Except for the enclosed space with hazardous substances (such as the inner space of closed container, the inner space of fixed roof liquid storage tank, etc.), there is little zone 0.

② Zone 1 (Class 1 Hazardous Area) refers to the area where explosive gas, vapor or mist is expected to occur periodically or occasionally during normal operation.

③ Zone 2 (Class 2 Hazardous Area) refers to the area where explosive gas, vapor or mist do not appear during normal operation, even if they do occur only occasionally for a short time.

The level of explosion hazard area is mainly affected by the characteristics of release source and ventilation conditions. The level of continuous release is higher than that of periodic release; The level of periodic release is higher than that of accidental short-term release. Good ventilation (including local ventilation) can reduce the scope and level of explosion hazardous areas.

The scope and grade of explosion hazardous area are also related to factors such as dangerous vapor density.

(2) Hazardous environment of dust and fiber explosion

According to the frequency and duration of explosive mixing, such hazardous environment is divided into zone 10 and zone 11.

① Zone 10 (Grade 10 hazardous area) refers to the area where explosive dust and fiber occur continuously or frequently for a long time or a short time during normal operation.

② Zone 11 (class 11 hazardous area) refers to the area where explosive dust and fiber do not appear during normal operation and only occasionally appear in a short time during abnormal operation.

2. Explosion proof safety requirements

Electrical explosion is related to fire, and explosion occurs at the same time of fire. Therefore, in addition to the fire safety requirements, the explosion-proof safety shall also pay attention to the following points:

(1) Selection of explosion-proof electrical equipment

Electrical equipment in explosion hazardous environment shall be selected according to the hazard level of the installation site, the group and level of hazardous substances, the type and service conditions of electrical equipment. The group and level of electrical equipment selected shall not be lower than that of hazardous substances in the environment. When there are more than two kinds of hazardous substances, the hazardous substances with higher risk degree shall be selected.

In the explosion hazardous environment, portable electrical equipment shall be used or not used as much as possible, and pin seats shall be installed as little as possible.

(2) Installation of explosion-proof electrical circuit

In explosion hazardous environment and fire hazardous environment, the installation position, laying mode, conductor material, connection method, etc. of electrical lines shall adapt to the regional hazard level.

(3) Explosion proof safety technology

① Eliminate or reduce explosive mixtures

Eliminate or reduce explosive mixture, including closed operation to prevent leakage of explosive mixture; Clean up the dust on the site to prevent the accumulation of explosive mixture; Design positive pressure chamber to prevent explosive mixture from invading the area with ignition source; Open operation or ventilation measures shall be taken to dilute the explosive mixture; Fill the dangerous space with inert gas or inert gas to prevent the formation of explosive mixture.

② Isolation

Dangerous equipment shall be installed in different rooms, and blocking measures shall be taken on the partition wall. Motor partition drive, lighting lamp and glass window lighting are all isolation measures.

③ Eliminate ignition source

It mainly includes the following measures:

Select electrical equipment and design electrical circuits according to the characteristics of explosion hazardous environment and the level and group of hazardous substances.

Maintain safe operation of electrical equipment and electrical circuits. Safe operation includes that the current, voltage, temperature rise and temperature do not exceed the allowable range, including good insulation, good connection and contact, overall intact, clean, clear marks, etc.

④ Grounding measures

For grounding in explosion hazardous environment, attention shall be paid to:

Equipotential bonding shall be made for all uncharged metal objects;

If the low voltage is distributed by the grounding system, TN-S system shall be adopted instead of TN-C system;

If the low voltage is distributed by an ungrounded system, it system shall be adopted, and a protective device that can automatically cut off the power supply in case of one-phase grounding or serious leakage or an alarm device that can send out sound and light signals shall be installed.

Responsible editor; zl

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