Selecting Ex Concepts of Protection

The Explosive Atmospheres market is both lucrative and expanding, but certification requirements—and the level of scrutiny by both buyers and regulatory authorities—are increasing. To access this market, it is imperative that equipment manufacturers understand the specific design, manufacturing, and certification requirements for their products.

When a ‘Zone’ has been established, special precautions must be taken by the manufacturer to reduce the likelihood of ignition to an acceptable level—and, where necessary, use mitigation measures to reduce the consequences of an explosion. These special methods are typically achieved by applying defined EX concepts from published standards and usually require specially designed products. The ‘a’, ‘b’, and ‘c’ designations after the protection concept indicate the level of protection:

a = Zone 0/20

b = Zone 1/21

c = Zone 2/22

Selecting the correct concept (or often, a combination of concepts) is critical before any design or development takes place.

Examples of Commonly Recognised Ex Concepts of Protection

FLAMEPROOF: Ex da, db or dc

A method of protection where the equipment is contained within an enclosure capable of withstanding an internal explosion of a flammable gas or vapour without damage, and without transmitting the internal flame to the external explosive atmosphere through any joints or structural openings.

INTRINSIC SAFETY: Ex ia, ib or ic

A protection technique based on limiting the electrical energy within the apparatus and interconnecting wiring exposed to an explosive atmosphere to a level below that which can cause ignition—either by sparking or heating effects.

PRESSURISATION: Ex pxb, pyb or pzc

A method of protection using pressurised protective gas to prevent the ingress of an explosive atmosphere into a space that may contain an ignition source. If necessary, it includes continuous dilution of any atmosphere within that space that might contain an emission source.

INCREASED SAFETY: Ex eb or ec

A method of protection in which additional measures are applied to electrical apparatus to provide increased security against excessive temperatures, arcs, and sparks during operation.

LIQUID IMMERSION: Ex ob or oc

A method of protection where electrical apparatus is made safe by oil immersion, preventing ignition of an explosive atmosphere either above the oil or outside the enclosure. The oil acts as a barrier between the explosive atmosphere and the electrical components.

POWDER FILLING: Ex qb or qc

A method of protection where the enclosure is filled with granular material, so that if an arc occurs, it is unlikely to ignite the external explosive atmosphere.

ENCAPSULATION: Ex ma, mb or mc

A method of protection in which components that could cause ignition by sparking or heating are enclosed in a compound, preventing any contact with the explosive atmosphere.

NON-INCENDIVE: Ex nC or nR

A type of protection applied to electrical apparatus such that, under normal operation, it cannot ignite a surrounding explosive atmosphere—and any fault capable of causing ignition is unlikely to occur.

In addition to these commonly used electrical concepts, there are also protection methods for:

• Non-electrical equipment (Ex h)
• Optical equipment (Ex op is, op sh, and op pr)
• Dust-only atmospheres (Ex ta, tb, and tc)

Where no standard concept is suitable (which is very rare), special protection may be used (Ex sa, sb, and sc). However, this is a complex and challenging process.

Sean Clarke CEng MSc FIET is the General Manager of ExVeritas are a UK Government Appointed Body for UKCA ‘Ex’, an ATEX Notified Body and an IECEx Certification Body and Test Laboratory, ExVeritas offers design reviews to help determine which protection concepts are feasible for your equipment and training courses for equipment designers. www.exveritas.com for more information.