Explosion proof electrical construction is different from ordinary electrical construction, as it depends on the increased explosion-proof requirements of the environment in which it is located. According to national and industry requirements, we define an explosive environment as an environment where combustible substances such as gas, vapor, mist, or dust form a mixture with air under atmospheric conditions. After ignition, the combustion will spread to the entire unburned mixture. Areas where explosive gas environments or combustible dust environments occur in large quantities or are expected to occur in sufficient quantities to require specialized preventive measures for the structure, installation, and use of electrical equipment are called hazardous areas. Explosion proof electrical construction refers to a job that meets the qualifications, conditions, and professional personnel for explosion-proof electrical construction, and is carried out in explosive environments and hazardous areas with strong professionalism.
The basic knowledge that should be mastered in explosion-proof electrical construction includes the following points:
1、 Classification, grouping, and zoning of explosive substances and hazardous areas.
Explosive gases should be classified according to their maximum test safety gap (MESG) or minimum ignition current ratio (MICR), and should be grouped according to their ignition temperature; Combustible dust can be divided into two types based on its conductive properties: conductive dust and non-conductive dust. Combustible dust is grouped according to its lowest ignition temperature; Explosive hazardous areas are divided into two categories based on the physical state of explosive substances: gas explosion hazardous areas and dust explosion hazardous areas; According to the frequency and duration of explosive gas environments, hazardous areas are classified into three zones: Zone 0, Zone 1, and Zone 2; According to the frequency and duration of combustible dust/air mixtures, as well as the thickness of the dust layer, they can be divided into three zones: Zone 20, Zone 21, and Zone 22;
2、 Selection of explosion-proof electrical equipment for explosive hazardous areas.
The selection principle of explosion-proof electrical equipment is safety, reliability, and economic rationality. The selection should be based on the level of the explosive hazardous area and the category, level, and group of explosive hazardous substances. The specific selection table should refer to the standard AQ3009-2007;
3、 Installation of electrical circuits and explosion-proof electrical equipment in explosive hazardous areas.
The installation methods of electrical circuits in explosive gas environments can be divided into cable wiring and conduit wiring. Electrical circuits should be laid in areas with low explosion hazards or at a distance from the release source, avoiding places that are susceptible to mechanical damage, vibration, corrosion, dust accumulation, and hazardous temperatures. When avoidance is not possible, preventive measures should be taken. The selected low-voltage cables or insulated wires must have a rated voltage higher than the operating voltage of the line and not lower than 500V. The insulated wires must be laid inside conduits, etc. Specific training courses on explosion-proof electrical installation, maintenance, and repair can be attended;
4、 Inspection and maintenance of explosion-proof electrical equipment in hazardous areas.
In order to minimize the ignition hazard of electrical equipment used in hazardous areas, an initial inspection should be conducted on the devices and equipment before they are put into operation and handed over for acceptance upon completion of the project; To ensure that electrical equipment is in good condition and can be used in hazardous areas for a long time, continuous supervision and regular inspections should be carried out. Initial and regular inspections should be entrusted to safety production testing and inspection institutions with explosion-proof professional qualifications.
The inspection and maintenance of explosion-proof electrical equipment should be carried out by qualified professionals who meet the prescribed conditions. These personnel should receive professional training including various explosion-proof types, installation practices, relevant regulations and rules, as well as general principles of hazardous area classification. They should also receive appropriate continuing education or regular training, and have relevant experience and trained qualification certificates. Continuous supervision and regular inspections will be carried out in the future. Propose reasonable remedial measures and equipment replacement measures for maintenance requirements.
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