I. Area Classification for Explosive and Flammable Gas Atmospheres

Zone 0: Areas where explosive and flammable gas mixtures continuously, frequently appear for long durations or persist for extended periods under normal conditions, e.g., certain parts of oil drilling platforms. The persistence time of hazardous gases is typically ≥ 1000 hours per year.

Zone 1: Areas where explosive and flammable gas mixtures may occur under normal conditions, e.g., non-mining faces of coal mines, enclosed areas of petroleum and petrochemical facilities (with ventilation openings). The persistence time of hazardous gases in such areas is generally 10 to 1000 hours per year.

Zone 2: Areas where explosive and flammable gas mixtures are unlikely to occur under normal conditions, and only appear occasionally for short periods under abnormal conditions, e.g., open non-enclosed areas of petroleum and petrochemical facilities. The persistence time of hazardous gases is typically ≤ 10 hours per year.

II. Area Classification for Explosive and Flammable Dust Atmospheres

Zone 20: Internal areas of equipment and containers where combustible dust continuously or frequently occurs during normal operation, in quantities sufficient to form combustible dust-air mixtures and/or potentially form uncontrolled and extremely thick dust layers, e.g., internal areas of certain dust containers, storage hoppers, etc. The persistence time of combustible dust is ≥ 1000 hours per year.

Zone 21: Areas where combustible dust-air mixtures of flammable concentrations may be generated during normal operation, e.g., external areas of dust containers under specific conditions. The persistence time of combustible dust is 10 to 1000 hours per year.

Zone 22: Areas where combustible dust-air mixtures are generally not present during normal operation, and combustible dust only appears occasionally and persists for short periods solely under abnormal conditions, e.g., the exhaust outlets of ventilation holes of bag-type dust collectors in the event of malfunctions. The persistence time of combustible dust is ≤ 10 hours per year.

It should be noted that the classification of hazardous areas shall take into account a combination of factors including the quantity of explosive and flammable dust, explosion limits and ventilation conditions. Meanwhile, an area may be classified as a non-hazardous area if it meets specific criteria.

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