There are established engineering concepts recognised by the IEC for the design of electrical equipment for hazardous area applications. These engineering concepts are the basis of protection against the risk of fire or explosion from gas or dust.
Each concept is identified by a protection symbol. If a design relies on more than one concept all symbols are normally shown.
|Symbol & EN ref||Concept||Summary||Zone use||Category|
|Ex i EN 60079-11||Intrinsic safety||Limits energy of sparks & surface temperatures||0,1 & 2||1,2 & 3|
|Ex d EN 60079-1||Flameproof||Contains explosion quenches ﬂame||1 & 2||2 & 3|
|Ex e EN 60079-7||Increased safety||No arcs, sparks or hot surfaces||1 & 2||2 & 3|
|Ex p EN 60079-2||Pressurised||Keeps ﬂammable gas out||1 & 2||2 & 3|
|Ex m EN 60079-18||Encapsulated||Keeps ﬂammable gas out||0,1 & 2||1,2 & 3|
|Ex q EN 60079-5||Powder ﬁlled||Keeps ﬂammable gas out||1 & 2||2 & 3|
|Ex o EN 60079-6||Oil ﬁlled||Keeps hazard away from ignition source using inert oil||1 & 2||2 & 3|
|Ex nA EN 60079-15||Non-sparking||No arcs, sparks or hot surfaces||2||3|
|Ex nR EN 60079-15||Restricted breathing||Gasket restricts air movement||2||3|
|Ex nC EN 60079-15||Enclosed break||Sealed from air ingress||2||3|
The explosive nature of dust is generally classified into three groups.
|Symbol & EN ref||Concept||Zone use||Category|
|Ex t EN 60079-31||Protection by enclosure||20, 21 & 22||1, 2 & 3|
|Ex i EN 60079-11||Intrinsic safety||20, 21 & 22||1, 2 & 3|
|Ex m EN 60079-18||Encapsulation||20, 21 & 22||1, 2 & 3|
|Ex pD EN 61241-4||Pressurised||21 & 22||2 & 3
Concepts such as Ex i, Ex p, Ex t and Ex m have been split into a, b and c. This allows for a new type of protection called ‘EPL’ or Equipment protection level. For Gas this is Ga, Gb and Gc and for Dust Da, Db and Dc.
According to EN 60079-0 the EPL is the level of protection assigned to equipment based on its likelihood of becoming a source of ignition and distinguishes the diﬀerences between explosive gas atmospheres, explosive dust atmospheres and the explosive atmospheres in mines susceptible to ﬁredamp.
Ga and Ma - Very high level of protection
Gb and Mb - High level of protection
Gc and Mc - Enhanced level of protection