Hazardous Area Classification/Zone Classification

 

What is Hazardous Area Classification (HAC)?

Hazardous Area Classification is a method of analyzing and classifying the environment where explosive gas or dust atmospheres may occur. The primary purpose is to prevent ignition of these atmospheres by controlling the selection and installation of electrical and mechanical equipment.

The core principle is to define the probability that a flammable atmosphere is present, which then dictates the required safety level of equipment used in that area.

The "Zone" System (Based on IEC / ATEX Standards)

The Zone system is used extensively internationally (Europe, UK, Asia, etc.) and is defined by the IEC (International Electrotechnical Commission) standards, which are adopted in regions like the EU as ATEX directives.

It classifies areas based on the frequency and duration of the occurrence of a hazardous atmosphere.

For Flammable Gases, Vapors, and Mists (Zone 0, 1, 2)

Zone 0 An area in which an explosive gas atmosphere is present continuously, or for long periods or frequently. Very High More than 1000 hours per year ( > ~10% of the time).

Zone 1 An area in which an explosive gas atmosphere is likely to occur in normal operation occasionally. High Between 10 and 1000 hours per year (0.1% - 10% of the time)

Zone 2 An area in which an explosive gas atmosphere is not likely to occur in normal operation and, if it does occur, will only persist for a short period. Low Less than 10 hours per year ( < 0.1% of the time)

Examples:

 Zone 0: The inside of a closed process vessel or storage tank where the vapor space above a flammable liquid is always present.

 Zone 1: The immediate vicinity around a pump seal, valve flange, or sampling point where a release is possible during normal operation.

 Zone 2: An area where a leak from a well-maintained pipework system is highly unlikely and would be rapidly dispersed if it did occur.

For Combustible Dusts (Zone 20, 21, 22)

A parallel system exists for dusts, which can also form explosive atmospheres.

Zone 20 An area in which a combustible dust cloud in air is present continuously, or for long periods or frequently. Very High Inside a dust hopper, silo, or inside a milling machine.

Zone 21 An area in which a combustible dust cloud in air is likely to occur in normal operation occasionally. High Areas near filling/discharge points, conveyor belt transfer points.

Zone 22 An area in which a combustible dust cloud in air is not likely to occur in normal operation and, if it does occur, will only persist for a short period. Low Areas where dust may form a layer but a cloud is only formed by an abnormal event (e.g., a leak from a faulty seal).