Author : Ron Sinclair

17 December 2009

October’s general meeting of the IEC in Tel Aviv saw agreement on the new standard for Ex ‘s’ equipment and ongoing work for the transfer of the non-electrical standards work from CEN to IEC. Ron Sinclair was there and reports on these development

The requirement to develop a special protection Ex ‘s’ standard came from the IECEx Certification Scheme.  Europeans, using the ATEX Directive, have become used to allowing a degree of initiative in interpretation of standards, since the certification is against the Essential Health and Safety Requirements of the Directive, rather than against the letter of the standard. This is not to say that standards can be ignored, but under ATEX there is latitude available where strict compliance cannot be obtained because the product does not fit neatly into the scope of one or other of the standardised protection concepts. 

This is both a strength and a weakness of ATEX.  Innovation is possible, but how something is deemed to comply can become obscured and there might rightly be concern that, at the most, only one Notified Body has reviewed the process.

Although the standard for construction and the process for certification have to be dealt with in different documents, it should be understood that, if the Ex ‘s’ standard is published, it will be handled in a fairly rigid process within the IECEx Scheme.  Put in ATEX terms, one Certification Body would be involved with Category 3 equipment (EPL Gc or Dc), two bodies with Category 2 equipment (EPL Mb, Gb or Db) and three bodies with Category 1 equipment (EPL Ma, Ga or Da). 

Thus it can be seen that the IECEx Scheme will be giving a very much higher level of scrutiny than is afforded via ATEX where, for Category 3, there is no need to involve a Notified Body at all.

A plenary session of IEC TC31at the Tel Aviv meeting was very much a reporting session on progress in the various sub-committees, working groups, project teams (developing new standards) and maintenance teams (preparing new editions of existing standards). One of the more interesting developments was reported from the sub-committee for intrinsic safety. Because of health hazards, they are contemplating finding an alternative to cadmium as a material for use in the spark-test apparatus.  There is concern for the toxic exposure of the test engineers, both through physically handling the cadmium disk and from the vapour that is produced by the spark between the cadmium and the tungsten wires.  If the search is successful, we may have to get used to a change in all the standard curves.

Less than a week after the Tel Aviv, CLC-TC31 met in Dublin.  The Cenelec meeting is very different to the IEC equivalent, as nearly all the technical work is done at IEC level. Cenelec committees do have a significant responsibility in formulating the ATEX annexes for the IEC standards when published in their EN versions. 

There was only one real question for discussion in Dublin, but it is a subject which can directly affect every user and purchaser of Ex equipment in Europe. It is: What is meant by “state of the art?” 

Those who are familiar with the ATEX Directive 94/9/EC will recall the preamble to the Essential Health and Safety Requirements (EHSRs) outlined in Annex II.  This states that “technological knowledge” can develop rapidly and that such developed knowledge should be used as soon as possible in assessing compliance with the EHSRs.  This seems such a simple statement, but it is clearly capable of many different interpretations, and it is those differing interpretations which have led to delay in the publishing of the EN versions of the IEC standards.

Although there are shades of opinion between them, there are two diametrically opposing views.  Because there is little evidence of correctly designed, installed and maintained Ex equipment having been the source of explosions for many years, it can be concluded that all equipment made in accordance with any of the EN standards issued over the last 30 years is probably safe enough, and that developments in the standards have no effect on compliance with the EHSRs.

The body of stakeholders represented within the standards development system have concluded that changes in the standards are necessary to take account of technical developments and to clarify possible interpretations of the standards and that, therefore, the latest published standard represents the intent of the EHSRs.

The committee is currently awaiting a view on this from the European Commission, but in the meantime have agreed to set up a joint working group with CEN-TC305 (responsible for the non-electrical standards) to try and resolve some of these issues.  The problem is that some of the views are so entrenched that finding a solution by consensus may not be possible.

The view expressed by the UK government – having taken  soundings from  UK stakeholders –  aligns most closely with the second option. There is particular concern that otherwise, there can be a significant commercial distortion to the market by allowing continued sale of products which do not comply with the latest standards. 

Is it right, for example, that the manufacturer of an Ex n fluorescent light fitting can use a standard industrial acrylic diffuser  – which can pass a 2 Joule impact test when new  –  if the equipment was first placed on the market before 2003, but a manufacturer designing a competitive product today must use a significantly more expensive material, possibly polycarbonate, which can pass a 4 Joule impact test after the ageing process for high temperature and high humidity required by the current standard.

In the end, it comes down to the fundamental question: is the Directive about free and equal trade, or is it just about minimum safety levels?

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