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Voltimum UK managing editor James Hunt looks at what constitutes a hazardous area, as well as at related legislation, directives and training. He asks whether this specialist sector can provide business benefits for electrical contractors:
This article, therefore, concerns certain types of factory, chemical/process plant and petrochemical facilities, mines and places where explosives are stored. Their electrical installations must be safe when within any hazardous areas.
Generally, specialists carry out much hazardous area work, but there is plenty of scope for electrical contractors as long as they are suitably accredited. Such scope includes working in many hazardous areas, but not all - those in large petrochemical plant, for example, may be too complex for most electrical contractors. However, petrol station forecourts, fuel, chemical and vehicle storage areas and small industrial plant where there are hazardous areas are not too complex, in principle.
Enterprising but accredited electrical contractors could find significant business opportunities with such applications, as long as they've had suitable training.
As an example, the ECA has member companies that are contractor that work on a variety of hazardous area installations - both large and small. These are backed by a team of experts, and by the ECA's quality system, which includes its Warranty, Bond and Inspection on Demand - go to: www.eca.co.uk/industry-advice-and-research/downloads/technical-guidance-for-non-members-1/information-technology-electronics-and-controls-itec/hazardous-areas
But first, the basics…
Area classifications and zones:
Area classification is the division of a facility into hazardous and non-hazardous areas, sub-divided into 'Zones'. For flammable gases and vapours, these Zones are as follows:
- Zone 0 - A volume in which an explosive atmosphere is constantly present.
- Zone 1 - A volume in which an explosive atmosphere is likely to occur in normal operation.
- Zone 2 - A volume in which an explosive atmosphere is unlikely to occur in normal operation.
Broadly similar Zone classifications exist for combustible dusts - these are Zones 20, 21 and 22.
Selection of electrical apparatus by Zone:
In order to select suitable electrical apparatus according to Zone, first identify possible sources of release of flammable gas, vapour or dusts, how long such a release could occur and how often. Note that the maximum surface temperature of electrical (and other) equipment must not reach the ignition temperature of any gas, vapour or dust present. CENELEC and IEC helpfully provide suitable tables.
Following such considerations, a decision can be made on apparatus selection. Varying techniques are used to either keep hazardous mixtures away from ignition sources - sparks (electrical, static or otherwise), and any hot surfaces - or prevent ignition sources from occurring to start with.
There is not sufficient room here to list and fully explain all the types of apparatus suitable for hazardous areas. The Box (below) provides a useful first guide and illustrates the nomenclature used.
Some equipment examples:
There is an extremely wide range of hazardous area equipment available. The following are just a few examples:
ABB supplies a wide range electric motors and drives that comply with the ATEX Directive, such as the company's highly efficient explosion proof motors. ABB's 'ATEX Jargon Buster' publication helps motor users cut through the terms and definitions 'jungle'. To save a copy, click on: http://www04.abb.com/global/seitp/seitp202.nsf/0/80b84ec385c362f6c1256f2e0051252c/$file/ABB+ATEX+Jargon+Buster+-+for+INSTRUMENTATION+users.pdf
In terms of cable management, electrical conduit, fittings and glands provider Kopex carries the IECEx scheme certification, and can provide ATEX advice. Note that cable itself is not generally made to a hazardous area 'standard'. Instead, its safety depends on how it is chosen and used. Fire alarm cable, for example, could be laid in a sand-filled trough or in steel conduit. As long as ATEX-approved cable glands are used, the installation should meet hazardous area regulations.
Dimplex's flameproof heaters are ATEX-approved for hazardous Zones 1 and 2. The fully sealed units feature a direct electric element that has no contact with the ambient surroundings, there is no thermostat or user control, and no gases are contained.
For applications involving explosive dust, Eaton's Moeller Electric brand offers an extensive selection of pushbuttons, indicator lamps and other pilot devices from its RMQ-Titan range in ATEX approved versions. All are approved for use in dust areas Zone 22, Category 3 and are approved for Device Group II (all applications except mining).
A Schneider Electric PDF document, entitled 'Explosive atmospheres - ATEX Dust - The Essential Guide', examines hazardous areas in terms of dust and the ATEX Directive. It shows which Telemecanique detection, control, signalling, sensing, machine safety/IS and automation products may be safely used. See it at: http://dokumentacia.schneider-electric.sk/pdf/ATEX_katEN08.pdf
Testing and standards:
Electrical equipment for use in hazardous areas must be fully tested and certified by an independent authority, such as BASEEFA. The IECEx scheme meets the requirements of international standards and the Certified Equipment Programme provides a certificate of conformity. If the equipment concerned passes, it is issued with a certificate that allows safe use in a suitable Zone.
In addition to standards relating zones, see the following: BS EN 60079-101; IEC 60079-10, 14 and 17; BS EN 1127 Part 11; IEC 61241-1-2, 3 and 17; IEC 61892-7; EN 50281-1-2; and PR EN 50281-3.
The mandatory ATEX Directive applies to equipment that introduces energy, electrically or mechanically, into a potentially explosive atmosphere. Directive 94/9/EC covers equipment, while 1999/92/EC is concerned with worker safety. The main objective is to help create a single European market in goods and services, with identical requirements in every EU country.
Good training is essential:
For electrical contractors to carry out hazardous area work, they must fully understand the issues and be accredited. The NICEIC Group (www.niceic.org.uk) holds hazardous area training courses, as does the ECA (www.eca.co.uk), which also works with COMPEX (www.compex.org.uk) to develop courses. BASEEFA too (www.baseefa.com) holds a range of hazardous area and ATEX/DSEAR courses, as does Intertek (http://uk.intertek-etlsemko.com), and Sira Test & Certification (www.siracertification.com). Many manufacturers also provide such training.
Box - Apparatus for use in Zones
Equipment is notated as Ex plus the letter suffix concerned - eg: Ex d (sometimes shown as Ex'd'), which relates to flameproof enclosures.
Apparatus for use in Zone 0 - Intrinsic safety (ia) - intrinsic safety equipment limits electrical energy so that any sparks produced are of too low an energy to ignite a surrounding explosive atmosphere.
Apparatus for use in Zone 1 - Flameproof enclosure (d) - keeps any flames from overheated or failed equipment away from explosive fluids, gases or dusts; Pressurised apparatus (p) - an internal pressure is used to prevent any external explosive fluid, gas or dust from entering an enclosure; Powder filling (q); Oil immersion (o); and Encapsulation (m) - all techniques for keeping apparatus fully shielded from explosive fluids, gases or dusts (encapsulation typically for smaller apparatus); Intrinsic safety (ib) - already explained but for Zone 1 rather than Zone 0; and Increased safety (e) - increased safety equipment must: not spark/arc; have no hot surfaces; have no semiconductor parts; have high integrity electrical connections; have increased creepage between live parts and earth potential.
Many items of industrial electrical equipment can be certified as increased safety.
Apparatus for use in Zone 2 - Electrical apparatus already designed for use in Zone 0 or Zone 1; Electrical apparatus designed specifically for Zone 2; and Electrical apparatus complying with a recognised industrial electrical apparatus standard that does not normally produce arcs/sparks - such equipment must be suitably enclosed and be assessed by a qualified person.
Apparatus for use in Zones 20, 21 and 22 - Refer to EN 50281-1-2 and BSEN 61241-17, which relate to electrical apparatus for use in combustible dusts, and the protection of such apparatus by enclosures.