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According to the frequency and duration of explosive dust environments, the places 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 release source" 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 exist 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 a 20 zone situation in the workplace is prohibited.

Examples of places 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 other than certain parts of belts and chain conveyors;

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

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

In most cases, the scope of Zone 21 can be defined by evaluating the release sources related to the formation of explosive dust/air mixture environments.

Examples of places that may generate Zone 21:

1. When explosive dust/air mixture appears inside the dust container, frequent movement or opening of the nearest entrance and exit door to the external area of the dust container for operation;

2. When measures to prevent the formation of explosive dust/air mixtures are not taken, 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, outside the dust container;

4. Possible occurrence of explosive dust clouds (but neither persistent, nor long-lasting, nor frequent)Zhongnuo TestingInternal locations of containers, such as the interior of simple warehouses with long self-cleaning intervals (if only occasional loading and/or discharging) and the accumulation side of filters.

Zone 22: It is 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 places that may generate Zone 22:

1. If the exhaust port from the dust bag filter vent fails, explosive dust/air mixture may escape. A location near equipment that is rarely turned on, or a location near equipment that is prone to leakage due to dust emissions above ambient pressure based on experience; Pneumatic equipment, flexible connections may be damaged in nearby areas.

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

3. When measures are taken to prevent the formation of explosive dust/air mixtures, places generally classified as Zone 21 can be downgraded to Zone 22. This type of measure includes exhaust ventilation. At the loading and unloading points of the dust bag, the feeding belt, the sampling point, the truck unloading station, the belt unloading point, etcZhongnuo TestingMeasures should be taken in the vicinity.

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