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Classification of explosion-proof areas for explosive gas environments

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| 2022-08-11|Return

When encountering many companies, we find that many companies believe that the classification of hazardous areas for explosive gas environments is based on the reserves or properties of hazardous substances, dividing them into "Zone 0," "Zone 1," and "Zone 2." However, this is actually a misconception:

The classification of hazardous areas for explosive gas environments is mentioned in the standard documents "GB 50058-2014 Design Specification for Electrical Equipment in Explosive Hazardous Environments" and "AQ 3009-2007 Electrical Safety and Explosion Protection Specification for Hazardous Areas". However, the AQ 3009-2007 Code for Electrical Safety and Explosion Protection in Hazardous Areas also cites relevant viewpoints from the GB 50058-2014 Code for Design of Electrical Equipment in Explosive Hazardous Environments.

Firstly, the classification of hazardous areas for explosive gas environments is based on the frequency and duration of the occurrence of explosive gas mixtures, which are divided into Zone 0, Zone 1, and Zone 2. The zoning should comply with the following regulations:

Zone 0 should be an environment where explosive gas mixtures occur continuously or for a long time;

Zone 1 should be an environment where explosive gas mixtures may occur during normal operation;

Zone 2 should be an environment where explosive gas mixtures are unlikely to occur during normal operation, or where even if they occur, they only exist for a short period of time.

From this, it can be seen that the classification of hazardous areas for explosive gas environments is actually based on the duration of the presence of hazardous substances in the area, rather than the storage capacity of the substances.

Under certain specific conditions, even if there are hazardous substances in the area, it can still be classified as a non hazardous area. If one of the following conditions is met, it can be classified as a non explosive hazardous area:

Areas without a source of release and where it is impossible for combustible substances to enter;

The maximum concentration of combustible substances that may occur does not exceed 10% of the lower explosive limit value;

Near equipment that uses open flames during the production process, or near equipment where the surface temperature of hot components exceeds the ignition temperature of combustible materials in the area;

Outside the production plant area, an overhead pipeline area for transporting combustible materials is set up in the open or open air, but the valve location is determined according to specific circumstances;

When the hazardous area is judged to have good ventilation, the hazard level of the explosion-proof area can be reduced as appropriate; When there is poor ventilation, the danger level of the explosion-proof area should be raised.

The following places can be designated as well ventilated areas:

✔ Outdoor places;

✔ Open type buildings, where the size and position of openings on the walls and roofs of the building ensure that the ventilation effect inside the building is equivalent to that of outdoor areas;

✔ Non open buildings with permanent openings to provide natural ventilation conditions;

✔ For enclosed areas, provide at least 0.3 cubic meters of air per minute per square meter of floor area or at least 6 air changes per hour.

When mechanical ventilation is used, the impact of mechanical ventilation faults can be disregarded in the following situations:

✔ Install backup independent ventilation systems for enclosed or semi enclosed buildings;

✔ When the ventilation equipment malfunctions, preventive measures such as setting automatic alarms or stopping the process flow to prevent the release of combustible materials, or preventing the equipment from powering off.

In summary, the classification of hazardous areas for explosive gas environments is based on the duration of the presence of hazardous substances. Under specific conditions, the hazard level of the area can be reduced or even classified as non explosive hazardous areas.


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