Classification of Dust Zones According to the ATEX Standard
Dust clouds in hazardous areas (at concentrations above the minimum explosive concentration) are divided into three zones according to emission class (according to EN 60079-10-2:2009).
Zone 20
The 20 marking indicates the continuous presence of combustible dust in quantities sufficient to form an explosive mixture with air. In these zones, the ignition and detonation potential is particularly high. Typically, the operation of electrical equipment in these zones is prohibited, or the equipment is moved outside of Zone 20 to less hazardous zones 21 or 22. Thus, Zone 20 is an area with a continuous presence of dust, where the use of electrical equipment is prohibited. Molson supplies explosion-proof servomotors for Zones 21 and 22.
Zone 21
The II 2GD Ex d IIB T4 marking indicates that motors are intended for use in areas where combustible dust may form in quantities sufficient to form an explosive mixture with air, but not in quantities equivalent to those in Zone 20. The ignition and detonation potential is also high here.
Zone 22
The II 3 GD Ex nA IIC T3 marking indicates that an explosive atmosphere in the form of a combustible dust cloud is unlikely to occur under normal operating conditions. If it does occur, it will only last for a short time.
Factors Affecting Dust Explosiveness
The delineation of hazardous areas is often complex due to the numerous factors that need to be considered. Key factors include:
Physical properties of combustible materials—composition, particle size, volatility.
Concentration of gases, vapors, mists, and liquids in the surrounding environment.
Nature of emission sources—intensity and duration.
Ventilation conditions—availability and effectiveness of ventilation systems.
Measures to prevent the spread of gases, vapors, and mists.
Factors affecting the volatility of combustible materials.
Safety data for the production site.
Equipment and installation configuration—location and design characteristics.
MOSEN explosion-proof servo motors are designed to address all these factors, ensuring safe and reliable operation in hazardous environments. They meet stringent standards for Zones 21 and 22, where the risk of explosive mixtures is controlled but still requires special attention.
