The Cenelec EEx'e' Concept in Oil and Petrochemical Engineering
Authors: Bennett P.A. 
Published: October 2008

Although a long established practice throughout Europe initially covered by the individual standards of what is now the European community and now harmonised under Cenelec (Comite Europeen de Normalisation Electrotechnique) under standards EN 50-014-039 the EEx'e' concept for hazardous atmospheres is little known, little understood and, because of differing standards, little used on the North American Continent.

This is a pity because the application of the concept can make the engineering design of an oil or petrochemical plant, oil-rig etc. simpler and more cost effective in that zone classification can be significantly less onerous, cheaper and virtually maintenance free apparatus can be used. This means, particularly on offshore oil and gas platforms Chat substantial savings in cost can be effected by means of the possible top-side weight reduction achieved by its use.

These factors which are to the benefit of all should no longer be ignored by the major oil producing companies and the many competent engineers, consultants and contractors who serve them.

References, figures and bibliography appear at the end of the paper.

WHAT IS THE EEX'e' CONCEPT

First of all it may be advantageous to compare our supposedly 'widely different' standards.

1. Definitions:

IEC/Cenelec recognise three zones which are compared with an abbreviation of the NEC definitions as follows:

ZONE 'O' - IEC/CENELEC

An explosive gas or mixture is continuously present - or present for long periods.

ZONE 1 - IEC/CENELEC

An explosive gas or mixture is likely to occur in normal operation.

CLASS I DIVISION 1 - USA/NEC

In which ignitable concentrations of flammable gases or vapours exist under normal operating conditions or in which ignitable quantities of such gases or vapours may exist frequently because of repair or maintenance operations or leakage.

ZONE 2 - IEC/CENELEC

An explosive gas or mixture is not likely to occur and if it occurs will only exist for a short time.

CLASS I DIVISION 2 - USA/NEC

In which volatile flammable liquids or gases are handled, processed or used but in which the liquids, vapours or gases will normally be confined within closed containers or systems from which they can escape only in case of accidental puncture or breakdown.

Now, if we exclude European zone 'O' which is exclusively for mining applications, we can see that Cenelec zone 1 equates very closely to NEC Class I Division 1 and that Cenelec zone 2 equates to Class I Division 2 so our classifications are broadly similar. What apparatus are we allowed to use in our respective zones/divisions?

What now follows is a brief resum6 of the standards - for a more comprehensive study please refer to the standards.

IEC79-10/CENELEC ZONE 1 .

Flame-proof EEx'd', increased safety EEx'e' which houses non-incendive components and apparatus, intrinsically safe EEx'ia' and 'ib' pressurised EEx'p', oil immersed EEx'O', powder filled EEx'q' special protection EEx'S', encapsulated EEx'm' and any equipment suitable for zone 'O'.

NEC CLASS I DIVISION 1

Flame-proof (explosion proof) intrinsically safe, purged and oil immersion.