Atex introduced the concept of Categories and Equipment Protection Levels (EPL), partly as an attempt to simplify equipment selection.
|Atex Category||EPL||Equipment suitable for|
|1G||Ga||Zones 0, 1 & 2|
|1D||Da||Zones 20, 21 & 22|
|2G||Gb||Zones 1 & 2|
|2D||Db||Zones 21 & 22|
The are 6 Atex Categories, designated '1', '2' and '3' representing levels of Risk 'High' 'Medium' and 'Low' respectively each with either 'G' and 'D' for Gas and Dust.
Equipment is allocated a protection Level (EPL) of 'G' and 'D' then 'a', 'b' and 'c' representing the degree of protection dependant on a number of factors, particularly 'fault conditions. This concept1 has been around for a long time with intrinsic safety protection but now has been introduced into other protection techniques2 In simple terms to have a EPL of 'a' (for use in any zone) safety integrity must be maintained with 2 fault conditions, for EPL 'b' only 1 fault condition and EPL 'c' no fault conditions are considered.
Currently there is always a direct correlation based on each line of the table e.g. An area category 2G will be Zone 1 and equipment inside that area must have an EPL of Gb (or Ga which is a higher level of protection).
Whereas historically equipment was selected by Zone, the correct way is to specify the Category suitability or EPL required as this is more in line with risk assessment techniques.
E.g. for a low risk dust hazard specify an EPL Dc or suitable for Category 3D
Please refer to labels for examples of how these concepts go together.