Area Classification In Oil And Gas

Our today’s topic is Area Classification In Oil And Gas

Our topic” Area Classification” for analysing and classifying the environment where explosive vapour/gas atmosphere may occur to facilitate the proper selection, installation and use of electrical/instrument apparatus.

Area Classification

 DEFINITIONS:

HAZARDOUS LOCATIONS:

Hazardous locations are those locations, areas, or spaces where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fiber or flyings.

EXPLOSIVE ATMOSPHERE:

An explosive atmosphere means a mixture with air, under atmospheric conditions, of flammable substances in the form of gases, vapors, mists or dust in which, after ignition has occurred, combustion spread to the entire mixture.

FLAMMABLE ATMOSPHERE:

A flammable atmosphere is defined as having sufficient concentration of flammable gas, vapor, mist or combustible dust in the air under atmospheric conditions capable of being ignited.

 FLASHPOINT:

The flashpoint of a liquid is the minimum temperature at which the liquid gives off vapor in sufficient concentration to form an ignitable mixture with air near the surface of the liquid within the vessel.

HAZARDOUS VS. CLASSIFIED LOCATIONS:

Hazardous locations are described as classified locations or classified area because they have been classified.

AREA CLASSIFICATION:

Use of area classification system helps in:

1. Identifying the extent of areas where an explosive atmosphere may occur under normal and expected conditions.

2. Selecting electrical apparatus/instruments for such area.

3. Locating other equipment like heaters, boilers, etc

 AREA CLASSES:

In this system, areas are classified and grouped according to the flammable/combustible materials, which may be present.

Class – I Locations are those in which flammable gases or vapours are or may be present in the air in quantities sufficient to produce explosive or ignitable mixtures.

Class – II Locations are those that are hazardous because of the presence of combustible dust.

Class – III Locations are those that are hazardous because of the presence of easily ignitable Fibres.

AREA GROUPS:

Groups exist to permit classification of locations depending on the properties of flammable vapours, liquids or gases and to permit testing and approval of equipment for such locations.

Class I hazardous locations are divided into groups in such a way that each group contains materials of similar explosion characteristics.

GROUP – A: Atmosphere containing acetylene

GROUP – B: Atmosphere containing hydrogen, or gases or vapours of equivalent hazard such as manufactured gas.

GROUP – C: Atmosphere containing ethyl ether vapours, ethylene or cyclopropane.

GROUP – D: Atmosphere containing gasoline, hexane, naphtha, benzene, butane, propane, alcohol, acetone, benzol, lacquer solvent vapour or natural gas.

Class II locations are divided into three groups identifying the specific materials involved.

GROUP – E: Atmosphere containing metal dust, including aluminium, magnesium and their commercial alloys and other combustible dust whose particle size, abrasiveness and conductivity present similar hazards in the use of electrical equipment.

GROUP – F: Atmosphere containing combustible carbonaceous dust,

including carbon black, charcoal, coal, or coke dust that have more than 8% total entrapped volatiles or dust that have been sensitized by other materials so that they present an explosion hazard

GROUP – G: Atmosphere containing combustible dust not included in Groups E or F, including flour, grain, wood, plastic and chemicals.

Class III locations groups are not applicable in KNPC

LOCATION AS PER DIVISIONS:

Having decided that a location should be classified and having designated the gas or vapour as group A, B, C or D, the next step is to designate the location as per Division.

DIVISION 1 – Class I, Division 1 hazardous locations are defined (as per NEC code Article 500) as follows:

1. Those locations in which ignitable concentrations of flammable gases or vapours can exist under normal operating conditions.

2. Those locations in which ignitable concentrations of such gases or vapours may exist frequently because of repair or maintenance operations or because of leakage.

3. Those locations in which break down or faulty operations of equipment or processes might release ignitable concentrations of flammable gases or vapours and might also cause simultaneous failure of electric equipment.

DIVISION 2 – Class I Division 2 Locations are as follows:

1. Those locations in which volatile flammable liquids or flammable gases are handled, processed or used, but in which the liquids, vapours and gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or break down of such containers or system or in case the abnormal operation of equipment.

2. Those locations in which ignitable concentrations of gases or vapours are normally prevented by positive mechanical ventilation and which might become hazardous through failure or abnormal operation of the ventilating equipment.

3. Those locations which are adjacent to a class I, Division 1 locations and to which the ignitable concentrations of gases or vapours might occasionally be communicated. unless the communication is prevented by adequate positive ventilation from the source of clean air and effective safeguards against ventilation failure are provided.

Area Classification by ZONES:

Zone 0 – As a location in which ignitable concentrations of gases or vapours are present either (1) continuously or (2) for long period of time.

Zone 1 – Zone 1 locations are defined as follows:

1. Those locations in which ignitable concentrations of flammable gases or vapours are likely to exist under normal operating conditions.

2. Those locations in which ignitable concentrations may exist frequently because of repair or maintenance operation or because of leakage.

3. Those locations in which equipment is operated or processes carried on, of such nature that equipment break down or faulty operations could result in the release of ignitable concentrations. and also cause simultaneous failure of electrical equipment in a mode to cause the electrical equipment to become a source of ignition.

4. Those locations were adjacent to a Zone 0 location from which ignitable concentrations could be communicated. unless the communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

Zone 2 – Those locations in which ignitable concentrations of gases or vapours are not likely to occur in normal operations and if they do occur, they will exist only for a short period of time.

Zone 20 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in the air is present continuously, or for long periods or frequently.

Zone 21 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in the air is likely to occur in normal operation occasionally.

Zone 22 – A place in which an explosive atmosphere in the form of a cloud of combustible dust in the air is not likely to occur in normal operation but if it does occur, will persist for a short period only.

Author: Afnan Tajuddin

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