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How to divide the dust explosion-proof area into 20 zones, 21 zones, and 22 zones?

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| 2021-09-06|Return

According to the frequency and duration of explosive dust environments, the locations classified as explosive dust environments are divided into three zones.

The dust layer, precipitation, and accumulation of combustible dust should be considered as any other source of release that may form an explosive environment.

Zone 20: Places where combustible dust clouds in the air persist, persist, or frequently exist in explosive environments for a short period of time.

The scope of Zone 20 includes areas where explosive dust/air mixtures are present continuously or frequently in pipelines, production and processing equipment.

If there is a persistent explosive dust/air mixture outside the dust container, it is required to be divided into Zone 20. But creating 20 zones in the workplace is prohibited.

Examples of locations that may generate 20 zones:

1. Internal locations of dust containers;

2. Storage tanks, silos, etc., cyclone dust collectors and filters;

3. Dust conveying systems, except for certain parts of belts and chain conveyors;

4. Mixers, crushers, dryers, loading equipment, etc.


Zone 21: During normal operation, it is likely to exist in explosive environments in the form of combustible dust clouds in the air by chance.

In most cases, the 21 zone range can be defined by evaluating the release sources associated with the formation of explosive dust/air mixtures in the environment.

Examples of locations that may generate 21 zones:

1. When an explosive dust/air mixture appears inside the dust container, frequently move or open the external area of the dust container closest to the entrance and exit door for operation;

2. When no measures have been taken to prevent the formation of explosive dust/air mixtures, outside the dust container closest to the loading and unloading points, feeding belts, sampling points, truck unloading stations, belt unloading points, etc;

3. If dust accumulates and due to process operations, the dust layer may be disturbed to form an explosive dust/air mixture, the external area of the dust container;

4. Dust that may experience explosive dust clouds (but not sustained, long-lasting, or frequent)Zhongnuo TestingInternal areas of containers, such as the interior of simple silos with longer self cleaning intervals (if only occasionally loaded and/or discharged) and the accumulation side of filters.

Zone 22: Places that are unlikely to exist in explosive environments in the form of combustible dust clouds in the air during normal operation, and if present, it is only temporary.

Examples of locations that may generate 22 zones:

1. If the exhaust port from the ventilation hole of the dust bag filter malfunctions, explosive dust/air mixtures may escape. A place near a device that has been opened for a short period of time, or a place near a device that is prone to leakage due to dust spraying above ambient pressure based on experience; Nearby locations where pneumatic equipment and flexible connections may be damaged.

2. A storage bag containing many powdered products. During operation, the storage bag may malfunction, causing dust to spread.

3. When measures are taken to prevent the formation of explosive dust/air mixtures, areas generally classified as Zone 21 can be downgraded to Zone 22. These measures include exhaust ventilation. At the loading and discharging points, feeding belts, sampling points, truck unloading stations, belt unloading points, and other locations of the dust collection bagZhongnuo TestingMeasures should be taken nearby.

4. A place where the controllable (cleanable) dust layer formed may be disturbed and produce explosive dust/air mixtures. Only when the dust layer is cleared by cleaning before the formation of a hazardous dust/air mixture, is it considered a non hazardous area.


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