Introduction to Hazardous Area Classification

You may already know well about hazardous area classification or hazardous area enclosures within the plant site where you work. Or may be you have already heard about that term once in your lifetime. That’s no problem, because in this article we will uncover the essential matters behind hazardous area classification.

hazardous-area-enclosuresIf you have not known the hazardous area enclosures within your plant site, at first you have to know it. This information is commonly available in as built documents of your plant facilities. It is under electric chapter with sub-title “Hazardous Area Classification”.

This classification was made during the design phases of the plant facilities through risk assessment studies. So, you can use the as built document as reference.

Definition and Purposes

According to wikipedia, hazardous area is defined as a place where concentrations of flammable gases, vapors or dusts occur. Meanwhile, DSEAR defines it as a place where an explosive atmosphere may occur in quantities that require special precautions to protect the health and safety of workers.

Such classification is made in order to identify area with potential atmospheric explosive hazards that require special precautions to prevent fire and explosion. By this definition, there will be areas with high potential of explosive atmosphere and areas in which explosive atmosphere may occur occasionally or in abnormal conditions. The hazardous area classification is divided into zones.

The term special precautions used in hazardous area classification mean required precautions to control the source of ignitions within the hazardous area, related to the design, construction, installation and equipment use.

Zones in Hazardous Area Classification

Zones are determined based on frequency and duration of explosive atmosphere occurrence. In general, the zones in hazardous area classification are:

Gases, vapors and mists

Zone 0: includes area where explosive atmosphere containing the mixture of air and flammable gas, vapor or mist present continuously or frequently or for long period.

Zone 1: includes area where explosive atmosphere containing the mixture of air and flammable gas, vapor or mist probably happen in normal operation infrequently.

Zone 2: includes area where explosive atmosphere containing the mixture of air and flammable gas, vapor or mist probably happen in abnormal operation or for a short period.

Dusts

Zone 20: includes area where explosive atmosphere containing the mixture of air and combustible dust present continuously or frequently or for long period.

Zone 21: includes area where explosive atmosphere containing the mixture of air and combustible dust probably happen in normal operation infrequently.

Zone 22: includes area where explosive atmosphere containing the mixture of air and combustible dust probably happen in abnormal operation or for a short period.

Hazardous Area Equipment

Selection of equipment has to be done according to the zones in hazardous area enclosures. It is done in order to control the equipment not to become ignition sources. Hazardous area equipments are categorized into category-1 for Zone 0 or Zone 20, category-2 for Zone 1 or Zone 21 and category-3 for Zone 2 or Zone 22.

The term equipment is applied both for fixed equipment and mobile equipment that are operated in the hazardous area. In general, all equipments installed within that area shall be explosion proof type. As examples, explosion proof equipments are explosion proof heaters, explosion proof flashlight, and explosion proof fittings.

Hazardous area equipment or explosion proof equipment has special label that needs to be ensured before making any selection to get the most suitable type for the hazardous area.

explosion-proof-typeThe label or marking mentions the explosive protection symbol “Ex” in a hexagon, category number of equipment (1, 2 or 3), letter G (for gas, vapor or mists) or D (for dust) and other safety related information such as temperature rating (T) and gas group.

Conclusion

After reading this article, you should understand and know exactly the hazardous area enclosures within your plant site. Second, you have to ensure that all equipments installed in the hazardous area shall be explosion proof equipment. Third, special safety precautions have to be taken to control ignition sources in area classified as hazardous area both in normal plant operation, emergency shut down and maintenance period.

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