Explosion proof electrical refers to electrical equipment used in environments containing flammable and explosive substances, designed with relevant explosion-proof measures to prevent accidents caused by ignition sources such as sparks, arcs, or high temperatures due to the equipment itself.
Here are some basic knowledge of explosion-proof electrical:
Classification and grouping of flammable and explosive substances
Flammable and explosive gases are classified into IIA, IIB, and IIC based on their maximum test safety gap (MESG) or minimum ignition current ratio (MICR)
Combustible dust can be divided into conductive dust IIIC, non-conductive dust IIIB, and combustible fly ash IIIA according to their conductivity characteristics
Classification of Hazardous Areas
According to the physical state of flammable and explosive substances, they are divided into two categories: gas hazardous areas and dust hazardous areas.
Gas hazardous areas are divided into three explosion-proof zones based on the frequency and duration of gas environment occurrence: Zone 0, Zone 1, and Zone 2.
Zone 0: A place where gas mixtures occur continuously, frequently, or for a long time under normal circumstances, such as certain parts of an oil drilling platform. Dangerous gases typically exist for at least 1000 hours per year.
Zone 1: Places where gas mixtures may occur under normal circumstances, such as non mining faces in coal mines, enclosed areas in petroleum and petrochemical industries (with ventilation openings), etc. The existence time of hazardous gases in this area is generally between 10-1000 hours per year.
Zone 2: Under normal circumstances, gas mixtures are unlikely to occur and only occasionally occur for a short period of time under abnormal conditions, such as in non enclosed areas of petroleum and petrochemical plants (outdoors). The duration of existence of hazardous gases is usually ≤ 10 hours/year.
Dust hazardous areas can be divided into three explosion-proof zones: Zone 20, Zone 21, and Zone 22, based on the frequency and duration of combustible dust/air mixtures and the thickness of the dust layer.
Zone 20: Places and container interiors where combustible dust continuously or frequently occurs during normal operation, and its quantity is sufficient to form a mixture of combustible dust and air and/or may form uncontrollable and extremely thick dust layers. For example, internal areas of certain dust containers, storage tanks, etc. The existence time of combustible dust is ≥ 1000 hours/year.
Zone 21: Places where combustible dust and air mixtures with combustible concentrations may be generated during normal operation. For example, places outside dust containers under specific conditions. The existence time of combustible dust is between 10-1000 hours/year.
Zone 22: Under normal operation, combustible dust and air mixture generally do not appear, and only occasionally appear under abnormal conditions, and only exist for a short period of time. For example, when the exhaust port of the dust bag filter ventilation hole malfunctions. The existence time of combustible dust is ≤ 10 hours/year.
Selection of explosion-proof electrical equipment
The selection principle is safe, reliable, and economically reasonable. The selection should be based on the level of the hazardous area and the category, level, and group of hazardous substances.
For example, the explosion-proof type "d" places the components that can generate spark arcs during normal operation of the equipment inside the explosion-proof shell. The explosion-proof shell can withstand internal pressure without damage and ensure that the energy of the flame gas inside is reduced when it propagates through the gap, which is not enough to ignite the gas outside the shell;
The increased safety type "e" improves the safety and reliability of equipment by taking measures to reduce the possibility of sparks, arcs, and dangerous temperatures; The intrinsic safety type "i" limits the energy released by the part of the circuit in the explosive hazardous area to a certain value to achieve the purpose of explosion prevention.
Specific selection can refer to relevant standards, such as GB/T 3836, AQ3009-2007, etc.
Installation of electrical circuits
The installation methods of electrical circuits in flammable and explosive environments can be divided into cable routing and conduit routing.
Electrical circuits should be laid in areas with low risk 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. For example, the selected low-voltage cables or insulated wires.
Equipment inspection and maintenance
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.
These inspections and maintenance should be carried out by qualified institutions that meet the prescribed conditions. They should undergo business training including various explosion-proof types, installation practices, relevant regulations and rules, as well as general principles of hazardous site classification. They should also receive appropriate continuing education or regular training, and have relevant experience and trained qualification certificates.
Regular inspections should be entrusted to safety production testing and inspection institutions with explosion-proof qualifications, with a time interval generally not exceeding 3 years. Enterprises should take timely corrective measures based on the inspection results and file the inspection report and rectification situation with the safety production supervision and management department.
Meaning of Explosion proof Mark
Explosion proof signs usually include the general explosion-proof sign "Ex" and other letters and numbers indicating the explosion-proof type, operating environment, temperature group, and other information.
For example: Explosion proof mark Ex db ib IIC T4 Gb,
This is a composite explosion-proof mark,
Ex means explosion-proof, and explosion-proof equipment needs to be printed with the Ex logo;
DBIB refers to the explosion-proof protection type adopted by the equipment, which means both explosion-proof and intrinsic safety;
IIC refers to equipment suitable for Class IIC gases in flammable and explosive environments (representative gases are hydrogen and acetylene);
T4 is the temperature group, which refers to the highest surface temperature of the equipment not exceeding 135 ° C;
Gb refers to the device protection level, applicable to Zone 1 and Zone 2.
When using explosion-proof electrical equipment in hazardous environments, relevant standards and regulations must be strictly followed to ensure production. At the same time, installation, inspection, and maintenance should be carried out by personnel to ensure that the explosion-proof performance of the equipment is always effective. If it involves the installation and use of specific explosion-proof electrical equipment, it is recommended to refer to relevant national standards, industry specifications, and equipment manufacturers' manuals.
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