Archive for August 2006

Equipment Protection Levels and all that

August 28, 2006

One of the evil side effects of the ATEX Directive is that the IEC feels compelled to follow its more whimsical requirements. However the IEC must maintain its independence and consequently it follows similar principles but modifies the marking.The most recent manifestation of this phenomenon is the creation of Equipment Protection Levels (EPLs], which are the IEC equivalent of the ATEX categories. The following table summarises a fairly complex situation.


Fortunately the EPL concept did not follow the displaced numerical marking of the ATEX categories. Using category 2 equipment in a Zone 1 still does not feel right. The EPLs follow the intrinsic safety level of protection indication of a, b and c in line with the level of protection afforded by the apparatus.The intention of the concept is to divide apparatus into categories of equal levels of risk and mark the apparatus so that a technician could decide whether the level of risk is appropriate to the location of the equipment. The fact that the technician would require an infinite knowledge of the plant operation to make such a judgement is completely ignored. [In practice no one person ever has all the information necessary to make a reasonable risk analysis]. The same technician is considered incapable of remembering which type of protection can be usually used in which Zone, hence the requirement to introduce EPLs. The most that marking can achieve is to raise doubts in the mind of the knowledgeable technician and cause him to ask questions about the suitability of the apparatus

The illusion that a piece of apparatus in isolation determines its level of safety is only held by standards writers who persist in trying to completely describe apparatus on the label. In the particular case of intrinsic safety it is the system which determines the level of safety which is achieved. For example an ‘ia’ apparatus will be marked with an EPL ‘Ga’ but if connected in an ‘ic’ system it will achieve a ‘Gc’ protection level and the label is misleading. Intrinsic safety is the method of protection which is most prone to creating this deception but all the other methods of protection suffer from the same problem to some extent.

The reality is that if IEC Ex certification is used, EPLs will emerge and will have to be marked. The marking requirements of pressure transmitter certified intrinsically safe for use in both gas and dust are incredible in every sense of the word. If by chance the device is made flameproof and dust tight then a high level of information overload is achieved and an extremely large label is required. At this point an invitation to license my pull-down labelling facility is offered.

Pull Down Label

Perhaps one day there will be support for my campaign to reduce the label to a certificate number and a website address. When this happens then the availability of full and up to date information on certification and use could be ensured. It might even be possible to satisfy the requirement to have information available in the language of the country where the equipment is being used