by Dr. Johannes Auret, Explolabs Consulting
Dr. Johannes Auret
Safety is generally considered expensive although, in theory, a higher product compliance level should result in savings. Real savings can be achieved with proper planning. This may be of some inspiration to those battling with costs.
Certification of all equipment for use in explosive atmospheres is controlled by ARP 0108, which is effectively part of legislation as it defines the legal requirements for certification of equipment for use in explosive atmospheres. According to this document, all explosion-protected (Ex) equipment shall have information assurance (IA) certificates issued by approved or accredited test
One case relates to standard motors converted to non-sparking motors (Ex nA) or dust-ignition protection motors (Ext/DIP). There are many of these motors in service and many of these do not have IA certificates for historical reasons.
The new edition of ARP 0108 (edition 2) deals with Ex certification and understandably states that this discrepancy is hazardous and must be resolved. This essentially means that such motors will have to be certified by ATLs at the first repair after release of ARP 0108 edition 2. Certification is not only an expensive process, but also very slow compared to the 24-hour breakdown recycle service which motor repairers offer.
Using standardised conversions to simplify compliance with the relevant standards may present a solution. For the standardised conversion of a TEFC induction motor to non-sparking, the conversion recipe might, for instance, require that a steel fan and sturdy steel cowl with a radial separation of at least 5 mm between fan and cowl be fitted if not already in place. This eliminates potential ignition hazards such as static and thermic sparking, frictional heat and hot particles, and impact damage on the cowl. The tests and assessments associated with evaluation of those ignition hazards are also negated by means of standardised conversion.
Standardised conversion recipes offer several benefits including that limited type testing (ATL testing) should be required for e.g. temperature ratings of T4 or better and ingress protection.
Assessment will be based on a conversion recipe endorsed by the certifying ATL based on a review of the complete set of requirements from the relevant standards. A normal IA certificate will be issued. The majority of assessments can be carried out at the repairer’s workshop.
The novelty of this approach is simply that the use of a limited number of standardised conversions, components and materials can make certification cheaper and faster.
The anticipated certification procedure should consist of five steps. Firstly, the repairer will apply for certification. The ATL will then develop a standardised conversion recipe, after which the ATL will type test and certify the converted range. This is a once-off process and the certificate will be valid for ten years. The repairer then draws up a conversion procedure per range. Ex features must be captured here using photos, sketches or drawings. Lastly, the repairer includes the range in the production quality assurance scheme (“mark scheme”) and in the list of mark-bearing products.
In conclusion, standardised conversion recipes for Ex nA and Ex t (DIP) motors may offer a safe, cost-effective way to keep these motors in service, provided users, repairers and ATLs co-operate with each other.
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