What is HAZARDOUS AREA CLASSIFICATION ? (PART A)

What is Hazardous Area?

A “hazardous area” is defined as an area in which the atmosphere contains, or may contain in sufficient quantities, flammable or explosive gases, dusts or vapours. In such an atmosphere a fire or explosion is possible when three basic conditions are met. This is often referred to as the “hazardous area” or “combustion” triangle. In order to protect installations from a potential explosion a method of analysing and classifying a potentially hazardous area is required. The purpose of this is to ensure the correct selection and installation of equipment to ultimately prevent an explosion and to ensure safety of life.

There are three necessary components for an explosion to occur ;

1. FUEL ( FLAMMABLE SUBSTANCE),

This needs to be present in a relatively high quantity to produce an explosive mixture (e.g. gas, vapours, mists and dusts).

2. OXYGEN,

Oxygen is required in high quantities and in combination with the flammable substance to produce an explosive atmosphere.

3. IGNITION SOURCE,

A spark or high heat must also be present.

When electrical equipment is used in, around, or near an explosive atmosphere that has flammable gases or vapors, flammable liquids, combustible dusts, ignitable fibers or flyings, there is always a possibility or risk that a fire or explosion might occur. Those areas where the possibility or risk of fire or explosion might occur due to an explosive atmosphere and/or mixture is often called a hazardous (or classified) location/area.

Currently there are two systems used to classify these hazardous areas; the Class/Division system and the Zone system.

The Class/Division system is used predominately in the United States and Canada, whereas the rest of the world generally uses the Zone system. However, the United States and Canada are trending more towards the Zone System.

Hazardous Area Zoning System

Hazardous locations per the Zone system are classified according to its Zone which can be gas or dust. For gas atmospheres electrical equipment is further divided into Groups and Subgroups.  Zone—The Zone defines the probability of the hazardous material, gas or dust, being present in sufficient quantities to produce explosive or ignitable mixtures.

Gas

1. Zone 0—Ignitable concentrations of flammable gases or vapors which are present continuously or for long periods of time.
2. Zone 1—Ignitable concentrations of flammable gases or vapors which are likely to occur under normal operating conditions.
3. Zone 2—Ignitable concentrations of flammable gases or vapors which are not likely to occur under normal operating conditions and do so only for a short period of time.

Dust

1. Zone 20—An area where combustible dusts or ignitable fibers and flyings are present continuously or for long periods of time.
2. Zone 21—An area where combustible dusts or ignitable fibers and flyings are likely to occur under normal operating conditions.
3. Zone 22—An area where combustible dusts or ignitable fibers and flyings are not likely to occur under normal operating conditions and do so only for a short period of time.

Group—Electrical equipment is divided into three groups .

1. Group I—Equipment intended for use in mines susceptible to firedamp (flammable mixture of gases naturally occurring in a mine).
2. Group II—Equipment intended for use in places with an explosive gas atmosphere other than mines susceptible to firedamp. Group II equipment is subdivided into three subgroups.- Group IIA—Atmospheres containing propane, or gases and vapors of equivalent hazard. – Group IIB—Atmospheres containing ethylene, or gases and vapors of equivalent hazard. – Group IIC—Atmospheres containing acetylene or hydrogen, or gases and vapors of equivalent hazard.
3. Group III—Equipment intended for use in places with an explosive dust atmosphere. Group III equipment is subdivided into three subgroups. – Group IIIA—Atmospheres containing combustible flyings. – Group IIIB—Atmospheres containing non-conductive dust. – Group IIIC—Atmospheres containing conductive dust.