How are explosion-proof areas classified exactly?

Class A and Class B explosion-proof areas are classified in accordance with building codes. Article 3.1.1 of these codes stipulates that the fire hazard associated with a particular type of production should be determined based on factors such as the nature and quantity of substances used or generated in that production, and it should be classified into Classes A, B, C, D, or E.

According to building codes, the classification is based on the fire hazard associated with production activities, not on the classification of explosion-proof areas. In my opinion, according to this approach, there should be categories such as devices or areas with Class A fire hazard in production, and those with Class B fire hazard. In the Code for Design of Electrical Installations in Explosive and Flammable Environments GB50058-92, clause 2.2.5 states that the classification of explosion-hazardous areas should be determined based on the level of the source of explosion and the ventilation conditions, and it must comply with the following regulations. I. First, the areas should be classified according to the levels of the following emission sources: 1. Areas with continuous-level emission sources can be designated as Zone 0 ； 2. Areas with primary release sources can be classified as Zone 1 ； 3. Areas with secondary release sources can be classified as Zone 2. This clearly indicates the name of the explosion-proof area

What the original poster referred to as a “Class A explosion-proof area” probably means a fire protection rating of Class A combined with an explosion hazard area

Explosion-proof zones are not equivalent to fire zones； There are national standards, IEC standards, and NEC standards for explosion-proof zones. The design manual lists the correspondences between different standards. Now there is also a 0 zone in NEC’s division

I believe the classification of fire resistance ratings can be based on Section 3 of the Petroleum and Chemical Industry Fire Protection Design Code, namely 3.0.1, which states that the fire hazard of combustible gases should be classified according to Table 3.0.1. Table 3.0.1 Classification of fire hazard for flammable gases. Lower explosion limit of mixtures of flammable gases with air: Class A – Hydrocarbon liquids and other similar liquids at 0.1 MPa; Class B – Flammable liquids other than those in Class A, with a flash point ranging from 45°C to 120°C. 3.0.3 The classification of fire hazard for solids shall be carried out in accordance with the relevant provisions of the Code for Fire Protection Design of Buildings (GB50016). 3.0.4 The fire hazard class of a device shall be determined according to the fire hazard class of the medium it handles, stores, or transports. 3.0.5 The fire hazard classification of a room shall be determined based on the fire hazard classification of the equipment located within that room. When equipment with different fire hazard categories is installed in the same room, the fire hazard category of the room shall be determined based on the equipment with the highest fire hazard category among them. However, when the proportion of area occupied by equipment with the highest fire hazard category is less than 5%, and in the event of an accident, the fire is not likely to spread to other areas or can be prevented from spreading through fire prevention measures, it may be classified according to the equipment with a lower fire hazard category. The classification of explosion protection levels can be determined in accordance with Article 2.2.1 of Section 2, \"Classification of Areas at Risk of Explosion and Fire\", in the Design Code for Electrical Equipment in Explosive and Fire-Hazardous Environments. The areas at risk of explosion and fire are classified into three categories and eight grades based on the likelihood and consequences of accidents, as well as differences in the degree of danger and the state of the substances present, so that appropriate measures can be taken to prevent explosions or fires caused by sparks, arcs, or dangerous temperatures from electrical equipment and circuits. The classification into three categories and eight grades is as follows: I. Explosive hazard areas for gaseous or vapor explosive mixtures in Category 1 are divided into three grades. 1. Areas of Class Q-1 where explosive mixtures can form under normal conditions ； 2. Areas of Category Q-2 that under normal conditions cannot form explosive mixtures, but can do so under abnormal conditions ； 3. Areas of Category Q-3 that under normal conditions cannot form explosive mixtures, but in abnormal conditions have a low likelihood of forming such mixtures. For example: the amount of explosive substances in that location is small, the density of such substances is low making it difficult for them to accumulate, the lower explosion limit is high, and these substances have a strong odor. II. Explosive hazard areas for Class 2 dust or fiber explosive mixtures are divided into two grades: 1. G-1 grade areas – areas where an explosive mixture can form under normal conditions ； 2. Areas of Grade G-2 that under normal conditions cannot form explosive mixtures, but can do so under abnormal conditions ； III. Third-class fire-hazardous areas are divided into three grades: In Grade H-1 areas, flammable liquids with a flash point higher than the ambient temperature of the area are generated, used, processed, stored, or transported during the production process, in terms of both quantity and arrangement. Places posing a fire hazard ； 2. H-1 class locations where, during the production process, suspended or accumulated combustible dusts or fibers cannot form explosive mixtures, but where their quantity and arrangement can pose a fire hazard ； 3. H-3 class areas: Areas where solid combustible materials, in terms of quantity and arrangement, pose a fire hazard. Note: ① Normal conditions refer to normal driving, operation, stopping, etc. (such as open loading and unloading) ； ②Abnormal conditions refer to accidental damage, misoperation, improper maintenance, as well as disassembly and repair of devices or equipment. Article 2.2.2 For the classification of certain locations, in addition to complying with the provisions of Article 2.2.1 of these specifications, the following rules shall also be followed depending on their specific circumstances: 1. For open or partially open buildings and structures, as well as outdoor installation areas with good air circulation, the classification level may be reduced by one tier after taking into account various factors such as specific gravity, flash point, and explosion limits. II. Under normal conditions, a gas or vapor explosive mixture can only be formed in localized areas of the premises, and such localized areas shall be classified as Q-1 level ； The remaining areas should be classified into different grades based on the range that explosive mixtures may reach under abnormal conditions. III. Poorly ventilated dead corners or depressions such as deep pits in areas prone to explosions, where explosive gas or vapor mixtures can accumulate, should be classified as Q-1 level. IV. If one of the following measures is in place, and there is a location that is sufficiently reliable, the level can be reduced by one tier: 1. A location equipped with continuously operating ventilators that ensure an adequate number of air exchanges within the area, with proper uniformity; and where, in the event of a failure of one of the ventilation units, there is still sufficient ventilation capacity available, or backup units that can be activated automatically ； 2. A facility equipped with automatic measuring instruments to detect any location within it where gases or vapors are escaping or accumulating, and which is capable of reliably issuing a signal or shutting off the power supply when the concentration of such gases or vapors approaches 50% of the lower explosive limit. V. The exhaust fan room serving areas with explosion hazards shall have the same hazard level as the areas from which air is to be exhausted. VI. Fan rooms that serve explosive hazardous areas and are separated by walls may be classified as non-explosive hazardous areas, provided that the air ducts leading from these rooms into the explosive hazardous areas are equipped with safety devices to prevent the intrusion of explosive mixtures. VII. The areas adjacent to the following devices that are frequently used in production can be classified as free from explosion hazards: 1. Devices that use open flames ； 2. Equipment that uses hot components, whose surface temperature exceeds the auto-ignition temperature of the explosive substances present in that area. 8. Areas where the amount of explosively hazardous materials used is small and operations are carried out within fume hoods or enclosures can be classified as areas without explosion hazards. 9. Areas where overhead pipelines for transporting explosive substances are installed outdoors or in open spaces, away from areas at risk of explosion, can be designated as areas free from explosion hazards; however, the valves in such areas shall be considered on a case-by-case basis. Article 2.2.3 The area boundaries of zones in areas where explosive mixtures of gases or vapors exist shall be designated in accordance with the following provisions; however, factors such as the quantity of explosive substances, their physical properties, and practical experience from similar facilities in other enterprises shall also be taken into consideration. I. Division of the area scope for explosive hazard areas in enclosed buildings and structures: 1. Inside enclosed buildings and structures, the area is generally defined on a room-by-room basis ； However, depending on the specific conditions of production, the area in question can be divided more precisely based on factors such as the size and height of the rooms, as well as the quantity and location of explosive mixtures ； 2. For buildings and structures in Q-1 category, the area within 3 meters (both vertically and horizontally) outside the windows that lead to the outdoors can have its requirement reduced by one level (Figure 2.2.3-1). 3. For buildings and structures in Q-2 category, the area within 1 meter (both vertically and horizontally) outside the doors and windows that lead to the outdoors can have its requirement reduced by one group (Figure 2.2.3-1). II. Division of the area at risk of explosion in open or partially open buildings or structures: 1. For filling stations for flammable liquids, as well as combustible liquids with a flash point equal to or lower than the ambient temperature of the area, the affected zone generally includes the interior of buildings and structures, as well as an area within 15 meters along the shortest horizontal distance from their open surfaces, and within 3 meters vertically above those open surfaces (Figures 2.2.3-2, 2.2.3-3) ； 2. For enclosed process units containing flammable gases, flammable liquids, or flammable liquids with a flash point equal to or lower than the ambient temperature of the location, it generally refers to the space within 3 meters (both vertically and horizontally) along the shortest path inside buildings and structures as well as outside open areas (Figure 2.2.3-4). III. Division of the area at high risk of explosion for outdoor installations: 1. For filling stations for flammable liquids, or combustible liquids with a flash point equal to or lower than the ambient temperature of the area, it generally refers to the space within 15 meters horizontally and 7.5 meters vertically from the filling port (Figure 2.2.3-5) ； 2. For enclosed process units containing flammable gases, flammable liquids, or flammable liquids with a flash point equal to or lower than the ambient temperature in the area, it generally refers to the space within 3 meters (both vertically and horizontally) outside the equipment enclosure (Figure 2.2.3-6) ； 3. For the safety valves, vent valves, and relief valves of process units that handle flammable gases, flammable liquids, or flammable liquids with a flash point equal to or lower than the ambient temperature of the area, the relevant area is generally the space within 3 meters (both vertically and horizontally) from the valve opening (Figure 2.2.3-6) ； 4. For storage tanks of flammable liquids, or those of combustible liquids with a flash point equal to or lower than the ambient temperature of the location, it is generally the area within 3 meters (both vertically and horizontally) outside the tank shell (Figure 2.2.3-6) ； When a protective dike is present, it generally refers to the space within 3 units (vertically and horizontally) outside the tank shell, as well as the space inside the elevated dike with a height equal to that of the dike. (Figure 2.2.3-7) Clause 2.2.4: Areas adjacent to explosive-hazardous areas and separated by a wall with doors; although these areas do not contain explosive hazardous substances, they are at risk of explosion due to the possible intrusion of explosive materials. Their classification shall be determined according to Table 2.2.4. Grade of areas adjacent to explosive hazard areas: According to Table 2.2.4, the partition walls should be solid and non-combustible, while the doors should be flame-retardant, equipped with sealing measures and automatic closing devices (such as springs). It is generally not advisable to install windows in partition walls. If it is necessary to open a window, it must be sealed, fixed, and made of non-combustible material. Note: ① The fire resistance rating of non-combustible materials as referred to in these specifications shall not be less than 1.5 hours. ②The fire resistance rating of the flame-retardant materials referred to in these specifications shall not be less than 0.75 hours. When arranging corridors or suites adjacent to areas classified as Q-1, Q-2, or G-1, the clear distance between the two door frames shall not be less than 2 meters. If the adjacent areas that may be invaded by the explosive mixture are non-open buildings and structures, and there is a large amount of space compared to areas with explosion hazards, the scope of the explosion hazard zone can be determined based on specific circumstances. The classification of areas adjacent to explosive hazard zones in underground projects should be determined based on specific circumstances. For example, in the case of the configuration of supply and exhaust ventilation systems that allows the wind pressure in areas adjacent to areas with explosion hazards to be higher than that in those hazardous areas, or when appropriate measures are taken to prevent explosive mixtures from entering adjacent areas, the provisions in Table 2.2.4 may be followed; otherwise, the hazard classification of the adjacent areas shall not be reduced. The above are merely personal opinions and for reference only. 2.2.4 If the table is not available for copying, it can be found in GB 50058-92.

I’m sorry; what I provided is based on the **standard GBJ58－83 (trial version) of the People’s Republic of China. The current standard for the design of electrical installations in explosive and fire-hazardous environments is GB50058－92. This is to make a correction.

I asked what was going on; it’s not written that way in my GB50058－92 standard. I thought you had provided the latest version