Equipment protection levels in the hazardous area

26 August 2008

Hazardous area equipment manufacturers are beginning to adopt equipment protection levels as described in IEC 60079-0:2007. Ron Sinclair explains how the users will soon see examples of the new forms of marking

Manufacturers are getting to grips with IEC 60079-0:2007 even though it has not yet appeared in its EN version. This means that purchasers and users of equipment, which include Equipment Protection Levels (EPLs) will be seeing a change in which their equipment is marked.

The EPL system has been with us for a couple of years, particularly for equipment meeting the requirements of IEC/EN 60079-26 intended for installation in Zone 0. However, the new Part 0 of the standard makes a minor alteration to the format given in the older Part 26, and it is relevant to look at the difference and why the new marking requirements have been introduced.

EPLs and ATEX
The use of the EPLs comes from a realisation in the international field that the ATEX Directive did get something right in principle. As more and more equipment is provided with complicated combinations of protection concepts, a single identifier is needed of the level of protection that can be assumed for that equipment. For ATEX, we have got used to Categories of Equipment and how those categories allow us to unambiguously select particular items of equipment for use in the defined hazardous zones. The fact that the ATEX User Directive 199/92/EC also allows a variation to the Zone/Category relationship, based on a true risk assessment, is a bonus.

EPLs and IEC
A few years ago, IEC TC31 recognised the benefits of this risk assessment approach and created an ad hoc working group to see how this could be moved into the international field. The group recognised that for many years intrinsic safety had had two levels of protection (Ex ia and Ex ib) for installation in different zones, and also that the encapsulation standard IEC 60079-18 was being revised to include Ex ma and Ex mb. The standards makers had never been particularly happy with the nomenclature of the ATEX Categories so – after a fair amount of deliberation and consultation – it was agreed to base the IEC equivalent on the existing protection levels ‘a’ and ‘b’ and to add level ‘c’ to be equivalent to ATEX Category 3. The definitions of IEC EPLs and ATEX Categories are slightly different, but for most purposes can be considered equivalent.

EPLs and marking
With the latest edition of IEC 60079-0 comes a brand new marking system, albeit with a number of familiar components. Apart from introducing EPLs, the standard also uses Group III for the first time to identify equipment intended for use in the presence of flammable dust. Group I remains identified with both the gas and dust hazards found in underground mines but Group II becomes limited to non-mining hazards of gas, vapour and mist. A major decision, intended to clarify the situation, is to ensure that gas and dust marking remains separate. As with ATEX, the prefixes M, G and D are used as part of the EPL marking to make sure that there is no confusion when different EPLs apply to gas, dust or mining situations for the same item of equipment.

The correspondence between protection concepts and EPLs is given in the latest installation standard IEC 60079-14, and is reproduced in the table on this page. It can be seen immediately that the use of EPLs solves problems for standards, which do not have their own protection concept symbol. Both new and old designations for some of the dust protection concepts are given in table 1.

Footnote
Baseefa’s managing director Ron Sinclair is chairman of BSI Committee GEL/31, responsible for the UK input to both European and International standards for Electrical Equipment for use in potentially explosive atmospheres. He is also chairman of Cenelec TC31 and is responsible for representing electrical standardisation interests at the European Commission’s ATEX Standing Committee. He makes a major input to BSI Committee FSH/23, which has responsibility for input to CEN for non-electrical equipment and protective systems.





Table 1: Correspondence of protection concepts and EPLs (please scroll down)

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