ATEX Explained

The Explosion Protection Regulations.

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To place equipment and protective systems intended for use in potentially explosive atmospheres on the market or into service in all EU member states, the equipment must carry an 'ATEX' certificate required by the EU directive 94/9EC. This new directive is more commonly known as the ATEX directive (from the French: ATmospheres EXplosives).

User Environment
ATEX concerns all products to be used in places where explosive atmospheres may arise, such as mixtures of air and flammable materials such as gases, vapours, mists and dusts.

Product
ATEX does not only concern electrical equipment, but all equipment and protection systems for us in potentially explosive atmospheres.

Scope
In the ATEX directive, conformity of products is complusory. The ATEX directive also covers explosive dust/air mixtures as well as gases.

Classification of equipment
The ATEX directive contains classification into groups and categories which are defined by the marking on the equipment.

Area Classification
Process plants are divided into Zones (European and IEC method) or Divisions(North American method) acording to the likelihood of a potentially explosive atmosphere being present.

Europen and IEC Classification Definition of zone or division North American Classification
Zone 0 (gases) An area in which an explosive mixture is continuously present or present for long periods Class I Division 1
(gases)
Zone 20 (dusts) Class II Division 1
(dusts)
Zone 1 (gases) An area in which an explosive mixture is likely to occur in normal operation Class I Division 1
(gases)
Zone 21 (dusts) Class II Division 1
(dusts)
Zone 2 (gases) An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time. Class I Division 2
(gases)
Zone 21 (dusts) Class II Division 2
(dusts)
Marking
The ATEX directive requires the product to be marked with the CE mark, the 'EX' mark and the equipment code as per the folliowing example:

II2G0344
ExII 2G Eexd IIB T4

Ex - Explosion proof in accordance with ATEX.
II - Equipment group: II surface industries.
2 - Category 2 equipment (suitable for us in Zone 1)
G - Gas: Suitable for atmospheres containing gas.
E - European certificate in accordance with harmonised standards.
Ex - Explosion-proof electrical equipment.
d - Type of protection is 'Flameproof enclosure'-.
II - Gas Group II - surface industries
B - Gas sub group B
T4 - Temperature class T4 (135 degrees centigrade surface temperature).


Alternatives to the above are:

Equipment Group
I for mines - Category M1 and M2
II for all other locations - Categories 1, 2 and 3.

Category
1 - Equipment that is intended for use in areas where an explosive atmosphere is present continuously for long periods or frequently.
2 - Equipment that is intended for use in ares where an explosive atmosphere is likely to occur in normal operation and must ensure a high level of protection.
3 - Equipment that is intended for use in areas where an explosive atmosphere is unlikely to occur in normal operation and must ensure a normal level of protection.

Gas
For gasses add the letter G
For dusts add the letter D

Type of protection
D = Flameproof
ia = Intrinsically Safe
E = Increased safety

Gas Group
I = Mines
II = Surface above ground industries

Gas Sub Group
A = less easily ignited gases eg propane.
B = easily ignited gases eg etheylene.
C = most easily ignited gases eg hydrogen or acetylene.

Temperature Classification
Hazardous areas apparatus is classified according to the maximum surface temperature produced under fault conditions at an ambient temperature of 40°C, or as otherwise specified. The standard classifications are as follows:
T1 = 450°C
T2 = 300°C
T3 = 200°C
T4 = 135°C
T5 = 100°C
T6 = 85°C


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