Original standard number HGJ 21-1989 HG 20687-1989 Design code for power supply in explosion and fire hazardous environment of chemical enterprises HG20687-1989 Standard download decompression password: www.bzxz.net

Ministry of Chemical Industry of the People's Republic of China
Design Standard
Electric Power Design Code for Explosion and Fire Hazard Environments in Chemical Enterprises
HGJ 21 - 89
14G17 208
"Electric Power Design Code for Explosion and Fire Hazard Environments in Chemical Enterprises" is a design standard approved and promulgated by the Ministry of Chemical Industry. The contents of this code include: general provisions, gas or steam explosion hazardous environment, dust explosion hazardous environment and fire hazardous environment, and are attached with two appendices, a reference and preparation instructions. This code was proposed by the Electrical Design Technology Center of the Ministry of Chemical Industry, compiled by China Saiqiu Chemical Engineering Company, and reviewed by the Electrical Design Technology Center of the Ministry of Chemical Industry. The editors are Zhu Songyuan, Chen Leshan, Liu Hanyun and other comrades. The chief reviewers are Yu Junren, Zhang Xiuzhen, Shen Junhan, Zhou Yisan, Zhu Junyuan and other comrades.
Ministry of Chemical Industry
Design Standard
Electric Design Code for Explosion and Fire Hazard Environments in Chemical Enterprises
Editor-in-Chief! China Chemical Industry
Approved!
Ministry of Chemical Industry
June 1389
Design Standard
HGJ21-89
Page 1 of 34 pages
1.1 The design of electrical installations in explosion and fire hazardous environments must truly implement the technical and economic policies of the state. It should also implement the principle of prevention first, take measures according to local conditions, and ensure the safety of life and property of the state and the people, with advanced technology and reasonable economy.
1.2 This code applies to the design of electrical installations in explosion and fire hazardous environments for new construction, protection and reconstruction. This code does not apply to the following environments and equipment: (1) underground mines where explosive materials (such as gunpowder, dynamite and detonating powder) are manufactured, used or stored; (2) electrical equipment such as electrolysis, electroplating and batteries that use electric energy for production and are directly related to the production process; (3) equipment that uses strong igniters (such as chlorine, stearic acid, etc.) and materials that can ignite without external ignition sources (such as metallic sodium, potassium, yellow phosphorus, etc.); (5) water and land transportation vehicles. 1.3 The design of electrical equipment in explosive and fire hazardous environments shall comply with the provisions of the relevant national standards and specifications currently in force.
2 Hazardous environments with gas or vapor explosions
2.1 Scope of application
This standard applies to the design of electrical equipment in which the following explosive gas mixtures may or may appear during production, processing, handling, transportation or storage:
2.1.1 Explosive gas mixtures formed by the mixture of flammable substances such as flammable gas, vapor or mist of flammable liquid and air under atmospheric conditions (hereinafter referred to as explosive gas mixtures); 2.1.2 Explosive gas mixtures formed by the vapor or mist of flammable liquid with a flash point lower than or equal to the ambient temperature and air;
2.1.3 Explosive gas mixtures formed by vapor and air when the flammable liquid is likely to leak and the material operating temperature is higher than the flash point of the flammable liquid. 2.2 Purpose
This part is to divide the explosion hazard area according to the frequency and duration of the occurrence of explosive gas mixture in the process of production, processing, handling, transportation or storage of flammable substances, so as to select electrical equipment, and put forward preventive measures for the setting of substations and distribution rooms, electrical lines and grounding, so as to minimize the possibility of the simultaneous occurrence of explosive gas mixture and ignition source caused by electrical reasons. 2.3 Definition of terms
2.3.1 Flash point (FLASH-POINT): Under standard conditions, the lowest temperature of liquid that can release enough gas to form an explosive gas mixture that can flash. 2.3.2 Ignition temperature (IGNITIONTEMPERATURE): According to the international test method, the lowest temperature that ignites the explosive mixture.
2.3.3 Ambient temperature (AMBIENTTEMPERATURE): refers to the average maximum temperature in the zone. Generally, it should be determined based on the local meteorological temperature, combined with the degree of construction of buildings and structures, heat sources and ventilation. The monthly average maximum temperature can be selected, or the "working zone temperature" of the heating and ventilation professionals can be used or based on the actual measured data of the corresponding regional kitchen and other production sites: 2.3.4 Flammable substances (FLAMMABLEMATERI.1L): refers to flammable gases, vapors, liquids and mists.
2.3.5 Flammable gas or vapor (FLAMMABLEGASORVAPOUR): When mixed with air in a certain proportion, it will form an explosive gas mixture. 2.3.6 Flammable liquid (FLAMMABLELIQUID): A liquid that can produce flammable vapors or mists under all operating conditions (this regulation stipulates that liquids with a flash point of 45°C or below are flammable liquids, and liquids with a flash point of 45°C are flammable liquids). 2.3.7 Flammable mist: flammable liquid droplets dispersed in the air. 2.3.8 Explosive gas mixture: a mixture of flammable substances in the form of gas, vapor, or mist mixed with air under atmospheric conditions. When ignited, combustion will spread throughout the entire range. 2.3.9 Explosive atmosphere: an environment containing an explosive gas mixture. 2.3.10 Explosive limits (1) LOWER EXPLOSIVE LIMIT T): When the concentration of flammable gas, vapor or thin air is above this limit, it can form an explosive gas mixture. (2) Upper Explosion Limit: When the concentration of flammable gas, vapor or thin air is below this limit, it can form an explosive gas mixture. 2.3.11 Hazardous Explosion Area (HAZARDOUSAREA): An area where the amount of explosive mixture that may appear in the near future is sufficient to require preventive measures to be taken for the structure, installation and use of electrical equipment. 2.3.12 Non-HAZARDOUSAREA: An area where the amount of explosive mixture that is expected to appear is not sufficient to require preventive measures to be taken for the structure, installation and use of electrical equipment. 2.3.13 Zone: All or part of an explosion-hazardous area. Note: According to the frequency and duration of the appearance of explosive contents, it can be divided into zones with different hazards. 2.3.14 Source of release: The location or point where substances that may release explosive mixtures are located.
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Note: When determining the source of release, destructive accidents (such as explosions, etc.) of process containers, large pipelines or storage tanks should not be considered. 2.3:15 Natural ventilation environment: The area where fresh air can replace the original mixture due to natural wind or temperature difference. 2.3.16 Artifactual Ventilation Atmosphere: An area where fresh air is used to replace the original mixture by fans, exhausters, etc. 2.4. Conditions for explosion and measures to prevent it 2.4.1 The following three conditions must exist simultaneously for an explosion to occur: (1) the presence of flammable gas, vapor or mist of flammable liquid; (2) the above substances are mixed with air and their concentration is within the explosion limit; (8) the presence of sparks, arcs or high temperatures sufficient to ignite the explosive mixture; 2.4.2 Basic measures to prevent explosions
(Work) The possibility of the three conditions that may cause explosions occurring simultaneously should be minimized. (2) First, the production process design should eliminate or reduce the generation and accumulation of flammable gases, flammable liquid vapors or mists. The specific measures are:
a. Use lower pressure and temperature in the process flow. Confine flammable substances to closed containers as much as possible and try to prevent drowning.
b. The process layout should limit and reduce the scope of the hazardous area as much as possible. Different levels of explosion hazardous areas and non-explosion hazardous areas should be separated in their own rooms or boundaries.
Use nitrogen or other inert gas protection to isolate flammable substances from the air.
(3) Prevent the formation of explosive gas mixtures and reduce the probability of them reaching the explosion limit. The following measures can be taken:
. Try to use open-air or open layout to facilitate air circulation in the area, h. Install necessary mechanical ventilation equipment,
c. Install positive pressure chamber,
d. Install automatic measuring instruments to measure the concentration of any explosive gas or vapor released or easily accumulated in the area. When the gas or vapor concentration approaches 50% of the lower explosion limit, it can reliably send a signal or cut off the power supply.
(4) To eliminate or control the possibility of sparks, arcs or high temperatures generated by electrical equipment, the following measures can be taken: 2. According to the level of the explosion-hazardous area and the level and group of the explosive gas mixture, use electrical equipment of the corresponding type or higher than the above level and group, b. Take effective preventive measures in the design of explosion-hazardous environment engineering. 2.5 Zoning of explosion-hazardous environment
2.5.1 The explosion-hazardous environment should be divided into zones according to the frequency and duration of the occurrence of explosive gas mixtures
(1) Zone 0: The area where the explosive gas environment appears continuously or will appear for a long time. 3
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Note: Except for enclosed spaces, such as sealed containers, trenches and other internal gas spaces, there are rarely 0 zones. Although mixtures above the upper explosion limit will not form an explosive environment, the environment that is within the explosion limit due to the entry of air should still be classified as 0 zone. For example: a flammable liquid storage tank with a top cover should be classified as 0 zone when the space above the filter surface is not filled with inflammable gas.
(2) Zone 1: A zone where an explosive gas environment may occur during normal operation. (8) Zone 2: A zone where an explosive gas environment is unlikely to occur during normal operation, and even if it occurs, it may only exist for a short time.
Note: ① Normal operation refers to normal start-up, operation, maintenance, removal of emergency materials for products, opening and closing of sealed equipment, and troubleshooting.
All factory equipment operates within its design parameter range during normal operation. ② In production, Zone 0 is extremely rare, and most of them are in Zone 2. Reasonable measures should be taken to minimize Zone 1 during design. 2.5.2 If one of the following conditions is met, it can be classified as a non-explosion hazardous area: (1) An area without a release source and where flammable substances may not invade, (2) An area where the maximum volume concentration of flammable substances may not exceed 10% of the lower explosion limit, (3) Equipment or hot parts that use open flames during the production process, and whose surface temperature exceeds the ignition temperature of flammable substances in the area, near equipment, (4) An overhead pipeline area for transporting explosive substances installed outside the production device or in the open (but its access door must be considered separately according to the specific situation).
2.6 Factors to be considered when dividing explosion hazardous areas 2.6.1 The impact of release sources and ventilation should be considered when dividing explosion hazardous areas. 2.6.2 Release sources can be classified according to the possibility of releasing explosive hazardous substances: (1) Continuous release source: A continuous release source that is expected to release for a long time or frequently release in a short time. For example: a. The surface of flammable liquid in a fixed position without inflammable gas, b. The surface of flammable liquid in direct contact with the air valve (applicable to oil and water separators) c. Free exhaust holes and other openings that frequently or permanently release flammable gas or vapor into the air. (2) First-level release sources: Release sources that release periodically or occasionally during normal operation, such as a. The seals of pumps, compressors and valves that release flammable substances during normal operation, b. The drainage system of process equipment installed on containers containing flammable liquids that release flammable substances into the space during normal drainage,
C. Sampling points that release flammable substances into the space during normal operation. (8) Second-level release sources: Release sources that will not release under normal operation, and even if they do, they will only release infrequently or for a short time, such as:
8. The seals of pumps, compressors and valves that are unlikely to release during normal operation, b. Flanges, connectors and pipe joints
c. Safety valves, exhaust holes and other openings that cannot release flammable substances into the space during normal operation, d. Sampling points that cannot release explosive hazardous substances into the space during normal operation. , (.4) Multi-level release source: A release source composed of two or three levels mentioned above and: 4
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a. Basically divided into continuous level or first level, b. Releases produced under different conditions, the area caused by these conditions is larger than the area determined by the basic level, but the frequency is less and the duration is shorter. For example, different conditions refer to different amounts of flammable substances released under the same ventilation conditions. If the amount of flammable substances released by the first level exceeds the amount of flammable substances released by the continuous level according to the frequency and duration, it can be further divided into the first level release source. If the amount of flammable substances released by the second level exceeds the amount of flammable substances released by the continuous level according to the frequency and duration, and if possible, exceeds the amount of flammable substances released by the first level, then a second level release source can be divided in addition to or instead of the first level. Similarly, for the release sources basically classified as the first level, if the second level of flammable material release exceeds the first level according to the frequency change and duration, then the second level release source can be separately classified. First level release source
Level release
Multi-level release source
(first level/second level)
Figure 2.6.2 (1) Various release sources of explosive gas or steam in the air are classified as examples of explosion hazard zones: 1. This figure is
8) Ma Tian environment:
6) Release source is close to the average level.
2. The shape and size of this area depend on many factors (see Section 2.7). HGJ21-89
Level Teaching
Second-level Release Source
Multi-level Release Source
(Pure Level + Less Level 1>
Figure 2.6.2 (2) Example of the division of explosion hazard zones for various release sources of explosive gases or vapors lighter than air Note: 1. This figure is: www.bzxz.net
Open air environment:
b) Release source above the ground:
c) Gas significantly lighter than air.
2. The shape and size of this area depend on many factors (see Section 2.7). 2.6.3 Ventilation can be divided into the following types:
(1) Natural ventilation. For example:
a, a typical open-air site in a production plant, including open-air structures, pipe racks, open-air pumping stations, etc., b. Considering the specific gravity of gas and steam, many appropriately arranged holes are opened on the walls and roofs of open-type buildings to ensure good air circulation, which can be used as an outdoor site, C. It is not open-type, but it has permanent ventilation holes set for ventilation purposes to achieve natural ventilation (generally less than open-type buildings).
Note: In some of the above examples, it is also necessary to consider factors such as buildings, structures and facilities that hinder ventilation. (2) General mechanical ventilation. For example:
a Mechanical ventilation equipment is installed on the wall or roof to improve the general ventilation in the building, b Mechanical ventilation equipment is installed at appropriate locations to improve the general ventilation of open-type buildings in the area. 6
(8) Local mechanical ventilation. For example:
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8. Exhaust system for process equipment or storage containers that continuously or periodically release flammable gases or vapors, b. Supply and exhaust air used in poorly ventilated areas to remove flammable substances. (4) No ventilation. No measures are set up to replace the original air with fresh air, for example: the building has no permanent vents.
(5) Good ventilation. For example:
a. The air flow of natural ventilation can easily dilute the explosive hazardous substances to less than one-quarter of the lower explosion limit, b. Mechanical ventilation can achieve the same effect as the above natural ventilation, and closed or temporarily closed buildings are equipped with independent backup ventilation systems.
Note: For buildings with flammable liquids, the mechanical ventilation should not be less than six air changes per hour. For buildings with flammable bodies, natural ventilation should ensure that the selected wind area is not less than 1m2 per 500m2 floor surface. 2.6.4 The relationship between the level of release sources and ventilation methods and the division and scope of explosion-hazardous areas is as follows: (1) Natural ventilation and general machine-line ventilation
Continuous-level release sources may lead to Zone 0, first-level release sources may lead to Zone 1, and second-level release sources may lead to Zone 2. However, good ventilation may reduce the scope of the explosion-hazardous area or make it negligible, or may reduce the level or even classify it as a non-explosion-hazardous area. Therefore, we should try to use open-air ventilation to provide good natural ventilation to reduce the risk and save investment. On the contrary, if the ventilation is poor or the wind direction is inappropriate, the scope of the explosion-hazardous area may be expanded, and the level may be increased.
Even in the case of only one level of release source, different ventilation conditions may make the area around the release source become different levels of zones.
(2) Local mechanical ventilation
Local ventilation is more effective than natural ventilation and general mechanical ventilation in diluting explosive gas mixtures, so it can reduce the scope of the explosion hazard zone (sometimes it can be reduced to a negligible level), or reduce the level, or even classify it as a non-explosion hazard zone.
(3) No ventilation
When the release source is in an unventilated environment, the level of the explosion hazard zone may be increased. A continuous or first-level release source may lead to Zone 0, and a second-level release source may lead to Zone 1. (4) Obstacles (including pits and dead ends) At obstacles, pits and dead ends, the level of the local area will be increased and the range will be expanded due to the lack of wind shelter. Obstacles such as rafts and walls may sometimes limit the diffusion of explosive gas mixtures, thereby reducing the range (here the diffusion of gas or vapor should be considered). 2.6.5 Impact of ventilation failure
The division of explosion-hazardous areas is determined according to the normal operation of the nearby equipment. Therefore, the impact of ventilation equipment failure on the level and scope of the explosion-hazardous area should be considered. However, this impact does not need to be considered in one of the following situations. (1) There is an independent backup ventilation system. (2) When the ventilation equipment fails, there are preventive measures to stop the release of flammable substances (such as automatically stopping the process flow, etc.).
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(3) When the ventilation equipment fails, consider the preventive measures to cut off the power supply to the electrical equipment. 2. The scope of the explosion-hazardous area
2.7.1 The scope of the explosion-hazardous area is mainly determined by the following parameters: (1) The amount of flammable substances released: If the release plate increases, its scope may increase. (2) Release rate: When the release rate is constant and the release rate increases to the rate that causes the flow, the released weakly flammable substances will be further released in the air, and the scope of the explosion will be reduced. (3) Concentration of the released explosive gas mixture: With the increase of the concentration of the released source or flammable substances, the scope of the explosion hazard zone may expand.
(4) The melting point of the flammable liquid (the initial stagnation point of the mixture) is the temperature of the vapor released, which is related to the corresponding gas pressure at the lowest liquid concentration. For comparison, this temperature can be expressed by the boiling point of the flammable liquid. The lower the boiling point, the larger the scope of the explosion hazard zone. (5) Lower explosion limit: The lower the lower explosion limit, the larger the scope of the explosion hazard zone. (6) Flash point: If the flash point is higher than the maximum humidity of the flammable fluid, an explosive gas mixture will not be formed. The lower the flash point, the larger the scope of the explosion hazard zone. Some compounds (such as hydrogenated iron compounds) do not have flash points, although they form explosive gas mixtures. In this case, the equilibrium liquid temperature at the saturated concentration corresponding to the lower explosion limit should be used instead of the flash point to compare with the corresponding maximum temperature of the liquid. (7) Specific gravity. The larger the specific gravity (with air as 1), the larger the explosion hazard zone. In order to divide the scope, this regulation will refer to gases or vapors with a specific gravity above 0.75 as substances with a specific gravity of air. (8) Ventilation volume: As the ventilation volume increases, the scope of the explosion hazard zone will be reduced. The scope of the explosion hazard zone can also be reduced by changing the layout of the ventilation system. (9) Obstacles: Obstacles can hinder ventilation, so it is possible to expand the scope of the explosion hazard zone. Obstacles may also limit the diffusion of explosive gas mixtures, so it is also possible to reduce the scope of the explosion hazard zone. (10) Liquid temperature. If the temperature is above the flash point, the humidity of the processed liquid parts will increase, and the scope of the explosion hazard zone will expand. However, it should be considered that due to the ambient temperature or other factors (such as the surface), the temperature of the released liquid or vapor may rise, but it may also fall. 2.7.2 Determination of the scope of explosion hazardous areas
The scope of explosion hazardous areas with explosive mixtures of gas or vapor shall be divided according to the following provisions: (1) Inside a building, the scope is generally determined by room. However, according to the specific production situation, if the indoor space is large and the amount of explosive mixture that may be released from the release source is small, it may be implemented in accordance with 2.7.2 (2) and 2.7.2 (3). (2) If there are gases or vapors heavier than air in the building and the following conditions are met, it is not necessary to divide it into rooms: (a) The air volume calculated from the space within 1m above the ground of the environment is sufficient to dilute the explosive gas or vapor equivalent to 3 times the maximum amount in the release room environment within 1 hour to below the lower explosion limit. (b) The natural ventilation in the room is not hindered, and the ventilation is changed at least twice per hour. (e) There are no pits or dead corners below the release source in the room that may cause the accumulation of explosive gas or vapor. (8) If there are gases or vapors lighter than air in the room, they may not be classified as rooms if the following conditions are met: (a) The air volume calculated from the space within 11m below the plane of the roof (flat roof) (2m8 below the highest point for the roof or inclined roof) is equivalent to 3 times the maximum amount of explosive gas or vapor released into the environment within 1 hour until it is diluted to the lower explosion limit. (b) Natural ventilation is not allowed in the room, and the ventilation is at least twice per hour. (c) There are no dead corners in the room where the explosive gas or vapor may accumulate at the source of release and at the top. (d) For open-air or semi-open buildings, the amount should be determined according to 2.7.3 based on the source level and ventilation conditions. (e) The maximum amount of explosive gas or vapor released into the environment mentioned above does not include the amount released in the event of a rupture caused by a catastrophic accident.
2.7.3 The examples for determining the level and range of explosion hazard test areas can be in accordance with the provisions of 2.7.4 to 2.7.12. The requirements must be in accordance with the following provisions:
(1) The typical examples are typical cases. The factors affecting the scope in 2.5.1 and the production conditions must be fully considered. The specific working conditions must be analyzed and judged by experience before the following examples can be used to determine the range.
(2) The release source in Figure 2.7.10 is the second release source. (8) Typical examples: The gas lift ratio is less than or equal to 0.75 and is considered to be a gas that is washed with air. The gas lift ratio is greater than 0.75 and is considered to be a gas that is washed with air.
(4) When dividing the explosion hazard area, the additional 2 zones must include: the ability to expand to 15 times the external volume, high selective bed or high operating pressure, etc.
2.7.4 Explosive gases are more likely to be in the air, and the production area is well ventilated. The level and scope of explosion hazard areas can be divided according to Figures 2.7.4 (1) and 2.7.4 (2). 7.5m
ground environment
research class (energy materials may be released from the place where they are released) 2.7.4 (1): explosive gases are in the air, and the production area is well ventilated (the release source is close to the ground) ground
underground environment
additional zone 2 (construction in the place where flammable materials may be released) Section 2.7.4 (2) explosive gases are more likely to be in the air, and the production area is well ventilated (the release source is above the ground) HGf21 -89
2.7.5 Explosive gases are heavier than air, and the production area is poorly ventilated. The level and scope of explosion hazard areas can be divided according to Figure 2.7.5.
Release source in enclosure
Unfavorable zone
Rutongtao
15mNote15m(Note)
m(Note)
Additional zone (it is recommended to be considered only where flammable substances may be released) Figure 2
Explosive gas is heavier than air, production area with adverse wind 2.7.5
Note: 15m from the release source, or 3m from the outside, whichever is greater. 2.7.6 Explosive gas is heavier than air, the level and scope of the explosion hazard zone of the storage tank can be divided according to Figures 2.7.6(1) and 2.7.6(2).
Storage tanks are hopeless when raising the radius of 1.5m, with a wave attenuation surface of 0
under the floor, such as a pit. The explosive gas is placed in the air. Storage tanks on the floor outside (fixed type) are installed on the ground. There is no choice but to choose an internal floating type
under the floor, such as a pit, a structure
Figure 2.7.6(2)
Explosive gas is placed in the air. Storage tanks buried outdoors (floating roof type) 2.7.7 Explosive gas is lighter than air. The grade and range of compressor workshops with good ventilation (no side walls at the bottom) can be divided according to Figure 2.7.7.
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