The big bang theory

The recent publication of a revised British Standard comes as a timely reminder to installers of electrical equipment in potentially explosive atmospheres to be aware of the requirements of the ATEX (ATmosphères EXplosible) Directive.

Although it is still two years before the statutory regulations embracing this Directive are enforceable, contractors may now be involved in projects that are not due for commissioning until after July 2003, when the Directive takes full effect.

While manufacturers appear to be fully aware of the ATEX requirements and the implications for their products, they feel that contractors are not as prepared. Clive Key, of hazardous area equipment supplier Walsall, supports this view with the news that to date the company has received few requests for ATEX approved equipment. John Broomer of manufacturer Redapt, would agree. "In particular," he says, "there is often a failure to appreciate the vital need to select the right accessories for ensuring the required integrity of explosion-proof equipment." The ATEX Directive, which lays down a whole raft of rules to ensure that equipment used in potentially explosive environments is not a health and safety threat, applies to all EU countries. It is implemented in Britain through The equipment and protective systems intended for use in potentially explosive regulations (SI 1996/192) which came into force on 1 March 1996. Until 30 June 2003, manufacturers have the option of complying with the new ATEX Directive or the existing regulations.

To meet ATEX requirements, equipment must comply with the harmonised European standards applicable to the installed environment. Among these is the recently published BS EN 50018: 2000, Electrical apparatus for potentially explosive atmospheres – flameproof enclosure 'd'. This supersedes EN 50018: 1994, which will be withdrawn in June 2003.

BS EN 50018 must be read in conjunction with EN 50014: 1997, Electrical apparatus for potentially explosive atmospheres – general requirements. This covers equipment in categories M2 and 2, which deal respectively with equipment installed in mines and equipment installed in areas where explosive atmospheres are likely to occur.

Sira Test & Certification runs training courses in the safe use of electrical equipment in hazardous areas. The company's Stewart Finch states that most of the changes incorporated in the revised BS EN 50018 standard will have no significant effect on equipment design or installation practice, as they "only reflect what is already current practice".

One change that contractors should note, however, is that the standard now covers Ex stopping plugs and thread adapters. These can be tested separately from the enclosures, certified as apparatus and fitted without further certification.

Adapters are used when the thread size of the cable gland or connection device is larger than, or the same size as, the entry thread of the enclosure. Reducers are used to alter the entry thread of an enclosure to accept a cable gland or connection device with a smaller thread.

Adapters and reducers without metric female threads are certified as components, and as such require further approval before they can be fitted to Ex enclosures. This applies to all products that have a 'U' at the end of their certificate number.

Thread converter manufacturer Redapt's John Broomer stresses: "When selecting Ex-certified accessories for use in hazardous areas, it is important to ensure that the products selected not only perform the task they are required to, but also maintain the overall integrity of the equipment into which it will be fitted.

"Accessories," he adds, "must be certified to a suitable method of protection, and for use in the same gas group as the equipment into which they will be fitted." Broomer warns that special attention should be paid to ingress protection when installing stopping plugs and thread adaptors into Eex e enclosures – the IP rating is often higher for Eex e equipment. He cites cases where an adapter or stop plug has been installed, which in effect lowers the IP rating required. To help overcome this problem, Redapt offers products that are approved EEx de and tested to IP66/68.

The impact resistance of the accessories must also be considered to ensure the integrity of the equipment, especially when specifying non-metallic Ex accessories. For long-term integrity of an installation, care should be taken in selecting appropriate materials. Account must be taken of any corrosive atmosphere present and the potential for corrosion brought about by mating dissimilar metals.

Walsall's Clive Key warns: "Contractors are not always aware that they cannot modify a piece of explosion-proof equipment, such as drilling extra entries into an EEx d enclosure or fitting an extra terminal into an EEx e box." Certification of flameproof equipment is based on the equipment as manufactured and detailed by the supplier. Unauthorised modification may invalidate the certificate and could produce dangerous operating conditions.

Typical unauthorised modifications include the use of an incorrectly sized or type of sealing plug; use of the wrong cable entry gland; and the use of screws for any purpose other than that originally intended – in other words do not attach cable brackets using cover fixing bolts.

Key continues: "Contractors are sometimes unaware that the certificate for an item of equipment covers the complete package, and that spare covers cannot be supplied to fit previously supplied equipment." He proposes the introduction of a system under which installation personnel must be accredited as having been properly trained.

Clearly, those contractors working in hazardous areas have to keep abreast of such issues. Get trained up now and give yourself a market advantage. With the likes of Sira's training courses, and the COMPEX training on installations in potentially explosive atmospheres offered by JTL among others, it's time to get up to speed on the big bang theory.