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Hazardous Locations Design Consulting


Understanding
Zones
and
Divisions

Not all "hazardous locations" are equally hazardous. In keeping with conventional risk management techniques, hazardous locations are classified - that is, designated - according to the severity of the threat.

In this context, "hazardous" means how likely it may be that an explosion may occur. There are many factors that play into this:

- the type(s) of explosive material present
- their physical properties
- how frequently they may be present
- how frequently an ignition source may present
- and - potentially - the severity of the consequences should an ignition occur.

For example, a confined location with a large and constant supply of easily-ignited fuel (such as a sugar mill) may be classified differently than a propane transfer station, which emits small quantities of fuel vapor into the atmosphere on an occasional basis.

To ensure consistency and safety, a systematic method of assessing and classifying hazardous locations is necessary.

To meet the need, different systems were adopted in different countries, with each country setting their own standards. This introduced significant barriers to serving an increasingly global market. Eventually, two systems came to dominate: the "Division" system and the "Zone" system.

The Division scheme was developed primarily in North America, and is still the primary one in use for those markets. Although both Canada and the USA are moving away from this system, existing installations may still demand Division-rated equipment.

The Division system consists of the following subdivisions and classifications:

- Class I: Explosive gas (or vapor)
- Class II: Explosive dust
- Class III: Explosive fibers (or flyings)

- Division 1: Explosive is always or nearly always present
- Division 2: Explosive is not normally present

Class I Groups:
- A = Acetylene
- B = Hydrogen
- C = Ethylene
- D = Propane

Class II Groups:
- E = Metal dusts
- F = Coal, coke and carbon black dusts
- G = Grain and plastic dusts

Class III:
- No Groups; all fibers and flyings (such as paper, plant and fiber) are included.

The Zone system was developed outside of North America, primarily by the International Electrotechnical Commission (IEC).

The goal of the IEC is to create internationally harmonized standards that apply worldwide. Part of the effort was applied to hazardous locations, with the Zone standard of classification being the eventual result.

The Zone system has been widely applied in European and international markets for many years. More recently, Canada and the USA have moved to adopt harmonized IEC standards as the basis for their national standards, making the IEC standards the basis for all future hazardous locations work.

The Zone system consists of the following subdivisions and classifications:

- Zone 0 – an area where explosive gases are present continuously
- Zone 1 – an area where explosive gases are likely to occur
- Zone 2 – an area where explosive gases are not likely to occur
- Zone 20 – an area where explosive dusts are present continuously
- Zone 21 – an area where explosive dusts are likely to occur
- Zone 22 – an area where explosive dusts are not likely to occur

- Group I: Methane (for underground mining industry only)
- Group II: Combustible gases
- Group III: Combustible dusts, fibers and flyings

The groups are further subdivided as follows:

- Group IIA: Propane
- Group IIB: Ethylene
- Group IIB + H2 – Hydrogen
- Group IIC – Acetylene
- Group IIIA – Combustible fibers
- Group IIIB – Non-conductive combustible dust
- Group IIIC – Conductive combustible dust

The Zone and Division systems are parallel, but not identical. The primary difference is in the equivalency of Divisions and Zones, which is as follows:

Division system Zone system
Division 1 Zone 0
Zone 1
Division 2 Zone 2


As can be seen, there are rough equivalencies between Zones and Divisions. Class I, Division 1 covers Zones 0 and 1; Class I, Division 2 covers Zone 2. Thus, Division 2 and Zone 2 are equivalent, but Division 1 is not perfectly equivalent to either Zone 0 or Zone 1.

Equipment certified for a more stringent Zone or Division may also be used in a lesser Zone or Division. For example, Zone 0 equipment can also be used in Zones 1 and 2.

Go to Protection Techniques.
Go to Certification Standards.
Go to Understanding ATEX.
Go to Understanding IEC 60079.

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