ATEX & IEC Concepts Explained

ATEX Concepts Of Protection

Any industry that processes, buy uses or manufactures materials that may give rise to a flammable atmosphere (gas, page mist, liquid, dusts or even small fibres) may have a potentially explosive atmosphere. Where fuel and oxygen (normally the oxygen in air) are present in the workplace, potential ignition sources must be rendered safe to an acceptable level for the risk.

Industries that generate potentially explosive atmospheres classify the dangerous areas based on the likelihood and duration of the explosive atmospheres presence. This is referred to as a ‘Zone’ (Europe and NEC505) or ‘Division’ (NEC500).

When a Zone or Division has been established, special precautions must be taken by the manufacturer to reduce the likelihood of an ignition being present to an acceptable level (and possibly to use mitigation measures to lower the consequence of an explosion). These specials metods are normally achieved by applying defined ATEX concepst from published Standards.

Given the onerous nature of an explosion, special certification schemes have been set up to control the design and certification of equipment for potentially explosive atmospheres.  Although the schemes differ globally (some are mandatory under law, some are simply procurement specifications), the bases for design and certification is similar, and the schemes normally rely on empirical testing, constructional assessment and production control by a recognised Certification Body.

Manufacturers of electrical equipment (and non-electrical for Europe) must be aware that if they sell to industries that have potentially explosive atmospheres (the vast majority of industries) they may be asked for

‘Certification’ and this may necessitate having a product specially designed to ATEX Concepts and certified through a certification body (in some cases a Notified Body and in some cases 3rd party or self-certification, although self certification is rarely accepted within this field)

The Explosive Atmospheres market is both lucrative and expanding, but the level of certification requirements and the level of checking (both by the buyer and by the regulatory authorities) are increasing. In order to access this market it is imperative that equipment manufacturers understand the design, manufacture and certification requirements or both discrete apparatus and assemblies (rigs and skids) to ensure that the products are designed without adding unnecessary costs and that the products are certified on time and correctly. To facilitate this, Intertek can help with design advise, training and complete Global certification at multiple locations world-wide.

Examples of commonly recognised ATEX concepts of protection (with other scheme acceptance)

There are eight commonly recognised concepts of protection in Europe and under NEC505 for electrical equipment, there are four under NEC500 (Divisions).

ATEX Concepts – FLAMEPROOF

Europe, NEC 500 and NEC505

ATEX Ex dA method of protection where the equipment is contained within an enclosure which will withstand an internal explosion of a flammable gas or vapour that may enter it, without suffering damage and without communicating the internal flame to the external explosive atmosphere, through any joints or structural openings in the enclosure. The enclosure will be designed for a particular gas grouping.

ATEX Concepts – Intrinsically Safety – Apparatus or System

Europe, NEC 500 and NEC505

A protection technique based upon the restriction of electrical energy within the apparatus and in the interconnecting wiring, exposed to a explosive atmosphere, to a level below that which can cause ignition by either sparking or heating effects. Because of the method by which intrinsic safety is achieved it is necessary that not only the electrical apparatus exposed to the explosive atmosphere, but also other (associated) electrical apparatus with which it is interconnected, is suitably constructed.

ATEX Concepts – PRESSURISATION

Europe, NEC 500 and NEC505

A method of protection using the pressure of a protective gas to prevent the ingress of an explosive atmosphere to a space that may contain a source of ignition and, where necessary, using continuous dilution of an atmosphere within the space that contains a source of emission gas, which may form an explosive atmosphere.

ATEX Concepts – INCREASED SAFETY

Europe and NEC505

A method of protection by which additional measures are applied to an electrical apparatus to give increased security against the possibility of excessive temperatures and of the occurrence of arcs and sparks during the life of the apparatus.  It applies only to an electrical apparatus, no parts of which produce sparks, arcs, or exceeds the limiting temperature of the materials, upon which safety depends, that are used in its construction.

ATEX Concepts – Type N (or N.I.) Protection (Non-sparking)

Europe, NEC 500 and NEC505

A type of protection applied to an electrical apparatus such that, in normal operation, it is not capable of igniting a surrounding explosive atmosphere, and a fault capable of causing ignition is not likely to occur.

ATEX Concepts – OIL IMMERSION

Europe and NEC505

A method of protection where the electrical apparatus is made safe by oil-immersion. In the sense that an explosive atmosphere above the oil or outside the enclosure will not be ignited.  The oil presents a barrier between the explosive atmosphere and the electrical apparatus.

ATEX Concepts – POWDER/SAND FILLING

Europe and NEC505

A method of protection where the enclosure of the electrical apparatus is filled with a mass of granular material such that, if an arc occurs the arc will not be liable to ignite the external explosive atmosphere.

ATEX Concepts – ENCAPSULATION

Europe and NEC505

A type of protection in which parts that could ignite an explosive atmosphere by either sparking or heating are enclosed in a compound in such a way that the explosive atmosphere cannot be ignited.  The compound provides a barrier between the electrical apparatus and the explosive atmosphere.

Definition of Categories /EPLs

Category 1 Equipment (Zone 0)  Ga, Da          

Must not have ignition sources that can become effective even in the event of a rare malfunction. Equipment in this category is intended for use in areas in which explosive atmospheres caused by mixtures of air and gases , vapours or mists or by air/dust mixtures are present continuously for long periods or frequently.

Category 2 Equipment (Zone 1) Gb, Db          

May have effective ignition sources (with a malfunction applied) protected by a concept listed in EN113463-1. Equipment in this category is intended for use in areas in which explosive atmospheres caused by gases, vapours, mists or air/dust mixtures are likely to occur.

Category 3 Equipment (Zone 2) Gc, Dc           

Must also be protected by a concept when ignition capable (relative to the gas or dust) in normal operation. Equipment in this category is intended for use in areas in which explosive atmospheres caused by gases, vapours, mists or air/dust mixtures are not likely to occur.

The categories in normal practice are equated to the suitability for Zones. Apparatus will be marked with the grouping and category in addition to the marking required by the individual protection.

 

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