Feature Hazardous Area Equipment
In the first of a two part feature, Toni Ott of Cooper Crouse-Hinds explains how important it is that engineers fully understand the implications of modifying enclosures to house electrical apparatus for use in explosive atmospheres
or end users and installers, it is vital that the implications of modi- fying enclosures are fully under- stood, whether it be sourcing Ex d flame-proof equipment for offshore oil platforms or onshore petrochemicals plants. It is important that end users fully appreciate what they are allowed to do with that Ex d enclosure so as not to invalidate the certification of the complete equipment.
The primary function of an Ex d enclosure is to prevent the propaga- tion of an internal explosion to the sur- rounding explosive atmosphere, and protecting the internal components from the environment, humidity, dirt, dust or water. With Ex d flame-proof enclosures, it is critical that the flamepath is not damaged. The exter- nal enclosure of any flameproof elec- trical equipment is designed to withstand an internal explosion. The enclosure joints therefore permit and control the resulting expansion of flames and hot gases - as these are relieved through the joints, preventing that explosion transmitting through to the external atmosphere. The relevant European (EN 60079-1) and interna- tional standards (IEC 60079-1) in addi- tion to EN/IEC 60079-0 ‘General Requirements’ apply.
In Europe, manufacturers and end users have to consult two directives - 94/9/EC covers equipment and protec- tive systems intended for use in poten- tially explosive atmospheres (ATEX) and is for the manufacturers of the equipment. For end users, Directive 1999/92/EC ‘Risks from Explosive Atmospheres’ (December 1999) outlines and harmonises the minimum require- ments for improving the safety and health protection of workers potentially at risk from explosive atmospheres. There is no directive covering the middle ground i.e. modifying an existing Ex d enclosure by neither a manufac- turer nor within the full responsibility of the employer (end user). Once Ex d equipment has left the manufacturer and its quality system (require- ment to affix the CE mark
on the type label), it is no longer the 16
responsibility of the manufacturer but lies with the end user.
Common pitfalls
Above: Toni Ott, manager, Test, Certification and Patents at Cooper Crouse-Hinds
Right: an open GHG64 enclosure showing the flame path
It is vital to increase awareness of rele- vant standards and education, as a lack of knowledge or inexperience can lead to mistakes. One of the most common mistakes made by end users and installers is to drill new cable gland entries into an Ex d enclosure
Understanding the standards F
is no longer valid.
Therefore, if any modifications are made to an Ex d enclosure and these are not within the responsibility and agreement of the equipment manufac-
turer, only two options exist: ●
1. New EC type examination certifi- cate with new type label is the responsibility of the legal entity modifying the equipment.
●
2. The end user takes full responsi- bility which means they also become responsible for any subsequent fail- ures of the enclosure that could lead to serious health and safety risks.
Other examples
Below: a GHG64 IIB enclosure with Ex e housing for customer connection
after or prior to installation. If space allows, an end user may decide to fit additional components into the enclo- sure such as a switch or an additional component with relevant power loss. This type of modification can affect the temperature class rating of the equip- ment’s enclosure or could lead to the overheating of other components inside the box, which in turn, may result in component failure or give rise to an ignition source.
In addition, these modifications could also weaken the mechanical integrity of the enclosure or lead to altered flame propagation, result- ing in excess of the maximum per- mitted reference pressures. Also, the results of the flame transmis- sion test performed during the EC type examination procedure could be negatively affected and a possi- ble internal ignition will not be safely controlled by the existing flame-proof enclosure from the external explosive atmosphere. Therefore, according to Directive 94/9/EC, only the manufacturer shall carry out such modifications. If the modification is carried out by another party, without control of the quality management of the original man- ufacturer, the marking on the equipment
Other examples of modifying an Ex d enclosure include accidentally damag- ing the flame-proof gap. When opening heavy enclosures, which typically involves unscrewing fasteners and lift- ing the cover, maintenance technicians must be careful not to inadvertently scratch or damage the flanges or threads. The cover should be lifted slowly and smoothly off the enclosure. Another common mistake when plac- ing the cover back on an Ex d enclosure is to fasten the screws to the wrong torque or to forget to replace screws. This is particularly important on Ex d gas group IIC enclosures (including IIB + H2
), where the tolerance of the flame- proof gap is typically down to 0.1mm. It is critical that all screws are tightened to the correct torque as specified by the manufacturer. If this isn’t done, the cover can bend and lead to an uneven flame gap. Of course, the same problem remains for IIB and IIA enclosures. With flame gaps, the impact of grease is also important. Often, there are mis- understandings amongst end users and installers about which greases should be used with an Ex d enclosure. In gen- eral, the grease that should be used is the one recommended by the manufac- turer. The message is clear for all cases - if you are in doubt, consult the enclo- sure manufacturer for advice and guid- ance on grease selection. The grease recommended by the manufacturer will have been tested at the applicable ambi- ent temperature range. Incorrectly selected grease may harden at low tem- peratures or may turn into an adhesive at higher ambient temperatures. Part two of this feature will appear in the May issue and will cover the rel- evant standards to consult and certifi- cation tests.
Cooper Crouse-Hinds
www.crouse-hinds.com T: 0247 630 89 30
Enter 209 APRIL 2013 Electrical Engineering
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