IEC
Area Classification
Area classification is the division of a facility into three-dimensional hazardous areas and non-hazardous areas and the subdivision of the hazardous area into ‘Zones’.
Hazardous areas may be sud-divided into three Zones as shown below.
| Flammable Gases and Vapour's | |
|---|---|
| Zone 0 | An area in which an explosive atmosphere is constantly present, or present for long periods. |
| Zone 1 | An area in which an explosive atmosphere is likely to occur in normal operation. (Rough Guide: 10 hours or more / year but less than 1,000 hours / year) |
| Zone 2 | An area in which an explosive atmosphere is not likely to occur in normal operation and if it
occurs it will exist only for a short time. (Rough Guide: Less than 10 hours / year) |
| Combustible Dusts | |
|---|---|
| Zone 20 | An area in which combustible dust, as a cloud, is present continuously or frequently, during normal operation, in sufficient quantity to be capable of producing an explosive concentration of combustible dust in a mixture with air. |
| Zone 21 | An area, in which combustible dust, as a cloud, is occasionally present during normal operation, in a sufficient quantity to be capable of producing an explosive concentration of combustible dust in a mixture with air. |
| Zone 22 | An area, in which combustible dust, as a cloud, may occur infrequently and persist for only a short period, or in which accumulations of layers of combustible dust may give rise to an explosive concentration of combustible dust in a mixture with air. |
For further information on the classification of hazardous areas see:
IEC/EN 60079-10 - Electrical Apparatus for Explosive Gas Atmospheres, Classification of Hazardous Areas.
Energy Institute (Formerly Institute of petroleum) - Model Code of Safe Practice in the Petroleum Industry. E115 Area Classification Code for Petroleum Installations.
Classification Society
A Classification Society may also enforce requirements for the design and installation of facilities. These requirements, which are in addition to statutory requirements, may influence the design and installation of the electrical systems. Classification Societies include ABS, DNV and Lloyds Register.
CENELEC And IEC
Design and Installation of Electrical Systems for Hazardous (Classified) Areas
There are numerous regulation codes, guidelines and standards for the design, selection and installation of electrical installation in potentially explosive atmospheres. These requirements are in addition to the requirements for installations in non-hazardous areas.
There are several types of protection, i.e. construction techniques, available for electrical apparatus in hazardous areas. The type of protection permitted will depend upon the applicable installation codes and rules to be adopted.
The selection of electrical apparatus should be in accordance with the following:
- Classification of the hazardous area.
- Temperature class or ignition temperature of the gas, liquid, vapour's, mist, dust or fibre.
- Where applicable, the gas, vapour or dust classification in relation to the group or subgroup of the electrical apparatus.
- External influences and ambient temperature.
Apparatus Selection According To Zones
Apparatus For Use In Zone 0
- Intrinsic safety ‘ia’
Apparatus For Use In Zone 1
- Electrical apparatus permitted for use in Zone 0, or
- Flameproof enclosure ‘d’.
- Pressurized apparatus ‘p’.
- Powder filling ‘q’.
- Oil immersion ‘o’.
- Increased safety ‘e’.
- Intrinsic safety ‘ib’.
- Encapsulation ‘m’.
Apparatus For Use In Zone 2
- Electrical apparatus permitted for use in Zone 0 and Zone 1, or
- Electrical apparatus designed specifically for Zone 2 (for example type of protection ‘n’) or
- Electrical apparatus complying with the requirements of a recognized standard for industrial electrical apparatus, which does not, in normal operation produce arcs or sparks. This equipment must be in an enclosure with a degree of protection and mechanical strength suitable for the environment and be assessed by a person who is familiar with the requirements of any relevant standards and codes of practice.
Apparatus For Use In Zones 20, 21 and 22
- IEC/EN 61241-0 - Electrical apparatus for use in the presence of combustible dust. General requirements.
and
- IEC/EN 61241-1 - Electrical apparatus for use in the presence of combustible dust. Protection by enclosures ‘tD’.
CENELEC And IEC
Apparatus Selection According To The Ignition Temperature Of Gas Or Vapour
The equipment must be selected so that its maximum surface temperature will not reach the ignition temperature of any gas or vapour that may be present.
| Temperature Class of Electrical Apparatus | Maximum Surface Temperature of Electrical Apparatus | Ignition Temperature of Gas or Vapour |
|---|---|---|
| T1 | 450°C | >450°C |
| T2 | 300°C | >300°C |
| T3 | 200°C | >200°C |
| T4 | 135°C | >135°C |
| T5 | 100°C | >100°C |
| T6 | 85°C | >85°C |
If the marking of the electrical apparatus does not include an ambient temperature range, the apparatus is only for use within an ambient temperature range from -20°C to + 40°C.
Apparatus Selection According To Apparatus Grouping
The grouping of gases and vapour's are classified into Group I and Group II categories. Group I is relevant to atmospheres containing firedamp (a mixture of gases, composed mostly of methane, found underground in mines).
Group II is intended for use in all other places with potentially explosive atmospheres. Group II electrical apparatus with types of protection ‘d’ and ‘i’ are further subdivided into apparatus group IIA, IIB or IIC. Electrical apparatus with type of protection ‘n’ may also be subdivided if it contains certain devices or components.
| Gas/Vapour Subdivision | Apparatus Subgroup Permitted |
|---|---|
| IIA (typical gas propane) | IIA, IIB or IIC |
| IIB (typical gas ethylene) | IIB or IIC |
| IIC (typical gases acetylene and hydrogen) | IIC |
Apparatus Construction Standards
IEC/EN 60079-0 - General Requirements
IEC/EN 60079-1 - Flameproof Enclosure ‘d’
IEC/EN 60079-2 - Pressurisation ‘p’
IEC/EN 60079-5 - Powder Filling ‘q’
IEC/EN 60079-6 - Oil Immersion ‘o’
IEC/EN 60079-7 - Increased Safety ‘e’
IEC/EN 60079-11 - Intrinsic Safety ‘I’
IEC/EN 60079-15 - Electrical Apparatus type ‘n’
IEC/EN 60079-18 - Encapsulation ‘m’
IEC/EN 61241-1 - Dust protection by enclosure
CENELEC And IEC
Installation Standards and Codes
There are numerous different regulations, codes, guidelines and standards for the design, installation and maintenance of electrical and non-electrical systems for use in potentially explosive atmospheres. The type of operational facility, geographic location, operator practice, local and national legislation authority having jurisdiction etc. will determine many of the design and installation rules permitted.
For further information on the design, selection and installation of equipment for use in hazardous areas see:
IEC/EN 60079-14 - Explosive atmospheres. Electrical installations design, selection and erection.
IEC/EN 61892-7 - Mobile and fixed offshore units . Electrical installations. Hazardous areas
IEC/EN 61241 - Electrical apparatus for use in the presence of combustible dust. Protection by enclosures ‘tD’.
Inspection Standards and Codes
For information regarding the installation and maintenance of equipment for use in hazardous areas, see:-
IEC/EN 60079-17 - Explosive atmospheres. Electrical installations inspection and maintenance.
