Dust places are divided into three areas: 20 zone, 21 zone and 22 zone.

District 20: in the process of the normal operation of combustible dust continuously or frequently, the number to form flammable dust air mixtures and / or may form cannot be controlled and very thick dust layer of places and the inside of the container.

District 21: in the normal course of operation, may appear dust quantities sufficient to form a flammable mixture with air single not included in District 20 places. The area includes places where dust is directly adjacent to the charge or discharge of dust, and where dust and normal operating conditions may produce combustible concentrations of combustible dust and air mixture.

District 22: under abnormal conditions, combustible dust clouds occasional exists and only a short time, or combustible dust occasional accumulation or there may be a dust layer and produce flammable dust air mixture but not classified as zone 21 places. If you can not guarantee the exclusion of combustible dust accumulation or dust layer, it should be divided into 21 areas.