For the above three standards, the first and most basic task for the user departments is to classify the explosion hazardous locations involved in this department. This is like a patient who visits, first of all through a thorough examination and the doctor's analysis of the symptoms after diagnosis. Accurate diagnosis is the basis for symptomatic treatment and safe drug use. This article specifically introduces the analysis of the national standard "Hazardous Location Classification" (GB 383614-2000).
1 Purpose of classification of hazardous locations
Hazardous area classification is a method of analyzing and classifying places where explosive gas atmospheres may occur. The purpose of site classification is to use led explosion-proof lamps in such explosion hazardous locations. The selection and installation of explosion-proof electrical appliances has sufficient safety and good economy. Because of the use of flammable substances in hazardous areas, it is difficult to ensure that explosive gas atmospheres never appear. Similarly, it is difficult to ensure that electrical equipment used in hazardous locations is never a source of ignition. Therefore, the type of explosion-proof electrical equipment with high safety performance should be selected in places where there is a high risk (ie where there is a high possibility of an explosive gas environment). Conversely, for sites where the risk is less severe (ie, places where the potential for explosive gas atmospheres is less likely), types of explosion-proof electrical equipment that are less secure (but still adequately safe) and relatively inexpensive may be selected.
2 The main content of the classification of hazardous locations
The classification of hazardous locations mainly includes two aspects:
(1) The hazardous area is divided into three areas according to the frequency and duration of the explosive gas environment
Zone 0: Sites where explosive gas atmospheres occur continuously or for a long time;
Zone 1: Locations where explosive gas atmospheres may occur during normal operation;
Zone 2: In normal operation, it is not possible to have an explosive atmosphere. If it occurs, it happens occasionally, and it is only a short-term existence.
(2) Determine the number and scope of hazardous locations
Because it is not enough to determine the area category of a dangerous place, the number of such dangerous places must be determined within and around the equipment, and the space range of each type of dangerous place must be determined. That is to say, the spatial range of the place should be accurate. The ration.
3 Basic Safety Principles for Classification of Hazardous Locations
(1) When designing equipment and installations for handling or storing flammable substances, the categories of hazardous locations should be minimized as far as possible. In particular, the number and scope of sites in Zone 0 and Zone 1 should be minimized. That is, as much as possible to make most of the dangerous places have become 2 District.
(2) The equipment used in the process shall be mainly a secondary release source. If this requirement is not met, the release source shall be released to the air with a very limited amount and release rate.
(3) After the categories of hazardous locations have been determined, they must not be changed arbitrarily. For the repaired process equipment, it must be carefully checked to confirm whether it can guarantee the safety level of the original design.
4 Classification of Hazardous Locations
According to the definition of a hazardous area, a hazardous area is an area where the explosive gas environment appears or is expected to occur in quantities sufficient to require special safety precautions for the structure, installation, and use of electrical equipment.
It can be seen from the definition that whether or not a place is a dangerous place is mainly based on whether or not an explosive gas atmosphere may occur at the place. The conditions for the formation of explosive gas atmospheres are whether the concentration range of flammable gas is within the explosive limit range. The concentration of flammable gases in the air is within this explosion limit (ie, the lower explosion limit and the upper explosion limit). An explosion can occur if the ignition source is encountered. Exceeding this range, a strong ignition source cannot ignite the explosion. In other words, any mixture that has a concentration lower than the lower explosion limit or higher than the upper explosion limit will not cause the flame to spread by itself when it comes into contact with the ignition source. When the concentration is lower than the lower explosion limit, excess air participates in the combustion reaction as an inert medium and consumes a part of the reaction heat, which acts as a cooling effect and hinders the self-propagation of the flame. Conversely, when the concentration is higher than the upper explosion limit, the amount of combustibles is excessive, ie, the amount of air. Insufficiency leads to incomplete chemical reactions. The amount of heat released by the reaction is less than the amount of heat lost, thus also impeding the spread of the flame.
From the above, it can be seen that the quantity of flammable gas in the site is the key to determine the hazard of the site, and the presence of flammable gas in the site mainly depends on the flammable gas release source and the ventilation conditions that affect the accumulation of flammable gas. Therefore, we can devise such a solution to the problem: the site is classified according to the size of its danger - the danger of the site depends on the number of explosive gas environments in the site - the explosive gas environment is the amount of flammable gas, That is, the explosion limit determines that the amount of flammable gas present depends on the ventilation conditions of the source and place of release.
5 Location Classification Methods
The core issue of location classification methods is the analysis of the probabilistic probabilities of explosive gas environments that may occur in a site. This requires the research and participation of experienced professionals. At the same time, it is necessary to accumulate and collect the operating status and environmental factors of each facility in the site. And other information. Therefore, the site classification should be determined by professionals who are familiar with the flammability properties, equipment and process conditions, and those engaged in safety, electrical, and other related engineering and technical personnel. The specific method is as follows:
(1) Finding and Determining Release Sources
The presence of flammable gases or vapours in the site may create an explosive atmosphere. Therefore, first of all, it is necessary to find out whether the storage equipment, processing equipment or pipeline containing flammable substances in the site may release flammable gas or vapor into the space, or whether air may enter the container and mix with flammable gas or vapor to form an explosive atmosphere. mixture.
Each device (such as tanks, pipes, pumps, compressors, etc.) should be considered as a potential source of release if it contains flammable substances. If they cannot contain flammable substances, it is clear that no explosive mixture will form around them. If this type of equipment contains flammable substances, but it is impossible to escape or leak into the site, it may not be regarded as a release source (for example, a jointless pipe installed in a certain space).
If it has been confirmed that the device will release flammable substances to the site, the release frequency and duration should be determined first, and the release source rating should be determined accordingly:
a Continuous release source: release source that is continuously released or expected to be released over a long period of time.
For example, the fixed top tank space and exhaust port; open flammable liquid container near the liquid level, etc., should be considered as a continuous release source.
b Level 1 release source: The source of release that is expected to be periodically or occasionally released during normal operation.
For example, during normal operation, it is expected that the seal of the pump, compressor or valve that releases flammable substances will be released to the surrounding area; the drain port on the container containing the flammable liquid; during normal operation, the flammable substance is expected to be released to the surroundings. Sampling points in the site; In normal operation, pressure relief valves, vent holes, or other openings that are expected to release flammable substances should be considered as a Class 1 release source.
c Class 2 release sources: In normal operation, it is not expected to release, if release is only an occasional and short-term release release source.
For example, in the normal operation, it is impossible to leak the seal of the compressor or valve; in normal operation, it is impossible to leak the flange, connector or pipe joint; in normal operation, it is impossible to release the sample of flammable substances to the surrounding places. Points, etc. should be considered as Level 2 release sources.
(2) Determine the type of area for hazardous locations
The types of zones that are divided into hazardous locations are mainly based on the release source levels and ventilation conditions in the site.
In general, continuous release sources form a hazardous area in Zone 0; Level 1 release sources form a Zone 1 hazardous location; Level 2 release sources form Zone 2 hazardous locations.
At the same time, the area division should be determined according to the ventilation conditions. When well ventilated, the area category of hazardous locations can be reduced. Conversely, if the ventilation is poor, the area of ​​the hazardous area can be increased. This is because the flammable gas or vapor released into the surrounding area will flow or diffuse through the air formed by the ventilation to dilute the concentration below the lower explosion limit.
(3) Determine the area of ​​hazardous locations
There are many factors such as the release rate of flammable gases or vapors, the lower explosion limit of gas, relative density, and ventilation conditions that affect the area of ​​hazardous areas. Therefore, after comprehensive analysis of their impacts, the regional scope of hazardous locations should be determined.
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