Division of the most dangerous environment and Cou

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Division of hazardous environment and electrical fire prevention and explosion-proof countermeasures

1) division of hazardous environment

in order to correctly select electrical equipment, electrical lines and various explosion-proof facilities, the size and level of the environmental hazardous area must be correctly divided

(1) dangerous environment of gas and steam explosion

according to the frequency and duration of explosive gas mixture, the hazardous environment can be divided into zone 0, zone 1 and zone 2

ventilation is an important factor in dividing explosion hazard areas. When dividing hazardous areas, the release sources and ventilation conditions should be comprehensively considered, and the following principles should be followed:

① for places with natural ventilation and general machinery used for ventilation of materials with extremely high hardness (such as cemented carbide, etc.), continuous release sources can generally form Zone 0 around, the first release source can form zone 0 around, and the second release source can form zone 1 around (including local ventilation), if there is no ventilation, The hazard level of the area should be improved. The first level release source may lead to the formation of zone 1, and the second level release source may lead to the formation of zone 2. However, good ventilation can reduce the scope of explosion hazardous areas, or it can be ignored, or its level can be reduced, or even classified as non explosion hazardous areas. Therefore, the release source should be arranged in the open air as far as possible to achieve good natural ventilation, so as to reduce the risk and save investment. On the contrary, if the ventilation is poor or the ventilation direction is improper, the scope of the explosion hazard area can be expanded, or the risk level can be increased. Even if there is only one level of release source, different ventilation methods may turn the range around the release source into areas of different levels

② local ventilation is more effective in diluting explosive gas mixture than natural ventilation and general mechanical ventilation in some occasions, which can reduce the area scope of explosion danger zone (sometimes as small as negligible), or reduce the grade, or even divide it into non explosion danger zone

③ when the release source is in an unventilated environment, the level of the explosion hazardous area may be increased. The continuous level or the first level release source may lead to zone 0, and the second level release source may lead to zone 1

④ at obstacles, pits, dead corners, etc., due to poor ventilation, the level of local areas should be improved and the scope should be expanded. On the other hand, barriers such as embankments or walls may sometimes restrict the diffusion of explosive mixtures and narrow the scope of explosion hazards (taking into account the density of gases or Vapors)

(2) dangerous environment of dust and fiber explosion.

the dangerous area of dust and fiber explosion refers to the environment around the production equipment in which the amount of suspended dust and fiber is enough to cause explosion, and the environment in which layered dust and fiber may form on the surface of electrical equipment and may cause spontaneous combustion or explosion. In gb420-1984 standard, according to the frequency and duration of explosive gas mixture, such hazardous environment is divided into zone 10 and zone 11

when classifying the dangerous environment of dust and fiber explosion, the amount of dust, the level of explosion limit and ventilation conditions should be considered. Experts from more enterprises are invited to give speeches! Open or partially open buildings or open plant areas with good airflow can be divided into low-level hazardous areas after considering the specific conditions of explosion limits and other factors. If a dust removal device with sufficient dust removal effect is installed, and when the dust removal device stops running, the process unit in explosive dust environment can be interlocked and shut down, and it can also be divided into low-level dangerous areas

the exhaust fan room serving the dust explosion hazardous environment should have the same risk level as the exhaust environment

when dividing the dangerous areas of suspended dust, we should consider the formation conditions, particle size, dust concentration, treatment methods of suspended dust in the environment, the outward leakage of dust from equipment or pipelines, the size of leakage, as well as the amount of dust used, the size of working space, whether there is an effective ventilation device, the failure of mechanical devices and the possibility of dust suspension, the configuration and isolation of mechanical devices, Sui situation and operating conditions, etc

when dividing the dangerous area of layered dust, the possibility of spontaneous combustion and the amount of dust deposition per unit time, the shape and configuration of mechanical devices, whether there is dust flying, whether the ventilation is good, dimensional deviation and appearance quality, cleaning times and cleaning difficulty should be considered. Special attention should be paid to the layered dust formed on the heating surface. If the thickness of the accumulative layer is large, it will also spontaneously ignite or even explode at a lower temperature

when dividing the hazardous areas adjacent to the plant, the hazard level and scope should be defined according to the specific situation of dust or fiber diffusion and deposition. Real time curve display and processing

for non open hazardous environments, hazardous areas should be divided by the production plant. For the open and semi open environment, if the area within the plant boundary is divided into zone 10, the horizontal distance outside the open surface is 7.5m (15m in case of poor ventilation), and the space 3M above the ground and roof should be divided into zone 11; If the area within the plant boundary is classified as zone 11, the space with a horizontal distance of 3M outside the open surface, 3M above the ground and 1m above the roof shall also be classified as zone 11

for concentrated outdoor devices, the space with a horizontal distance of 3M and a vertical distance of 3M outside the contour line of the device group shall be taken as the boundary of the zone or the boundary of zone 11; If there are 10 zones inside, the space with a horizontal distance of 15m and a vertical distance of 3M outside is divided into 11 zones

(3) fire hazard environment

the fire hazard environment is divided into zone 21, zone X and zone 23, which correspond to the old standard H-1, H-2 and H-3 fire hazard places one by one. They are the fire hazard environment with combustible liquid, combustible dust or fiber and combustible solid respectively

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