The area in the plant site can be classified into two classifications; hazardous area and non-hazardous area.
Some of you may already know well about hazardous area classification within the plant site where you work.
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But, the other may just hear about that term once in your career. That is no problem because in this post I will show you the important facts behind hazardous area classification.
If you have not known the hazardous area enclosures within your work area, then you must know it.
But, you ask me, “Where can I know it?”
Generally, this information is commonly available in as-built documents of your plant facilities. It can be found under the electric chapter with the sub-title “Hazardous Area Classification”.
Sometimes, it is also called by hazardous area classification chart or drawing.
This area classification was determined during the design phases of the plant facilities through a HAZOP study.
Hazardous Area Classification Definition and Purposes
If you refer to Wikipedia, you can find the definition of hazardous area as a place where concentrations of flammable gases, vapors, or dust 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 areas with potential atmospheric explosive hazards that require special precautions to prevent fire and explosion.
By this definition, there will be areas with a high potential of explosive atmosphere and areas in which explosive atmosphere may occur occasionally or in abnormal conditions. The area classification is divided into zones.
The term of special precautions used in hazardous area classification means required precautions to control the source of ignitions within the area, related to the design, construction, installation, and equipment use.
Understanding the Zones in the Hazardous Area Classification
The zones, in this case, are determined based on the frequency and duration of explosive atmosphere occurrence.
In general, the zones in hazardous area are divided into two major classifications, i.e. a zone for gases, vapors and mists, and a zone for dust.
Here are the explanations:
Gases, vapors and mists
Zone 0: includes the 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 the area where explosive atmosphere containing the mixture of air and flammable gas, vapor, or mist probably happen in normal operation infrequently.
Zone 2: includes the area where an explosive atmosphere containing the mixture of air and flammable gas, vapor, or mist probably happens in an abnormal operation or for a short period.
Zone 20: includes the area where an explosive atmosphere containing the mixture of air and combustible dust present continuously or frequently or for long period.
Zone 21: includes the area where an explosive atmosphere containing the mixture of air and combustible dust probably happen in normal operation infrequently.
Zone 22: includes the area where an explosive atmosphere containing the mixture of air and combustible dust probably happens in an abnormal operation or for a short period.
The Effect on Equipment Specification
The above area classification has a big effect on equipment specifications that will be installed inside the area.
The selection of equipment must be carried out according to the zones classification.
It is done in order to control the equipment not to become ignition sources.
Hazardous area equipment is 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 such area.
In general, all types of equipment installed within the hazardous area shall be explosion-proof type. As examples, explosion-proof pieces of equipment are explosion-proof motors, explosion-proof flashlight, and explosion-proof fittings.
Hazardous area equipment or explosion-proof equipment has a special label.
The 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.
Knowing the hazardous area in the workplace is very crucial. Since it will determine the equipment safety rating that you need to install. All the equipment must be explosion-proof type.
This classification also requires you to put special precautions against fire and explosion within the area.