Enclosing Ex risks

Redline versions of latest Standards for Ex-flameproof and pressurized enclosures published

By Morand Fachot

Flameproof enclosures for housing pieces of electrical apparatus is one of the well known and most used explosion protection techniques essential for use in explosive atmospheres, such as may be encountered on oil and gas platforms, in chemical and petrochemicals plants, grain silos and in many other sectors. The latest edition of IEC 60079-1:2014, also available in a Redline version, contains specific requirements for flameproof enclosures intended for use in explosive atmospheres. IEC 60079-2:2014, which has already been released, which covers pressurized enclosures for use in the same environments is another well-known explosion protection technique.

Offshore drilling platform (Photo: BP p.l.c.)
Offshore drilling platform (Photo: BP p.l.c.)

Putting a lid on flames

S+ IEC 60079-1:2014, the Redline version of the seventh edition of IEC 60079-1:2014, Explosive atmospheres – Part 1: Equipment protection by flameproof enclosures "d", has just been released. A Redline version clearly highlights all the changes to have taken place between the issue of the new edition and the previous one.

This seventh edition of IEC 60079-1 replaces the sixth edition, published in 2007, and constitutes a technical revision. It also supplements and modifies the general requirements of IEC 60079-0:2011, Explosive atmospheres -– Part 0: Equipment – General requirements

A flameproof "d" enclosure is an enclosure in which any parts that may ignite in an explosive atmosphere are placed. The enclosure has the internal strength required to withstand the pressure that will develop if a mixture explodes. A second characteristic of this form of explosion protection technique is that this type of enclosure prevents the flames from the internal explosion from transferring to the explosive atmosphere surrounding it. When incorporated with an appropriate IP rating, such enclosures may also protect their internal components from adverse environmental elements like humidity, dirt, dust or water This type of enclosure prevents the explosion from transferring to the explosive atmosphere surrounding it.

When incorporated with an appropriate IP rating, such enclosures may also protect their internal components from adverse environmental elements like humidity, dirt, dust or water such enclosures may also protect their internal components from adverse environmental elements like humidity, dirt, dust or water.

Protecting a critical path

Central to the efficacy of a flameproof enclosure is the flamepath or flameproof joint, defined in IEC 60079-1 as the "place where the corresponding surfaces of two parts of an enclosure, or the conjunction of enclosures, come together and which prevents the transmission of an internal explosion to the explosive gas atmosphere surrounding the enclosure".

Flameproof joints being a critical part of "d" enclosures, IEC 60079-1 lists the requirements and characteristics of the various types of flameproof joints (threaded, non-threaded, gaskets, etc.). It also describes the features of the sealed joints used when enclosures are cemented directly into a wall or into a metallic frame, and of the fused seals formed by applying molten glass to the metal frame of the enclosure.

Many key characteristics

IEC 60079-1 also gives details of the many design characteristics required to ensure flameproof enclosures meet the most stringent safety requirements. These include:

  • Supplementary requirements for shafts and bearings
  • Light-transmitting parts
  • Breathing and draining devices which form part of a flameproof enclosure
  • Fasteners, associated holes and blanking elements and openings
  • Materials and mechanical strength of enclosures
  • Entries for flameproof enclosures (threaded, non-threaded holes, sealing devices, etc.)

The Standard also lists additional requirements for components and subsystems that may form parts of, or be used in, enclosures such as switchgear, the various types of suitable primary and secondary batteries, doors, lampholders and lamp caps.

The proof of the enclosures is in the testing

For flameproof "d" enclosures to comply with the necessary stringent constraints, tests have to be carried out. IEC 60079-1 sets out the requirements for various type and routine tests, including explosion containment, flame transmission along with mechanical and sealing tests.

All these make for a very comprehensive Standard, as would be expected given the type of environments in which these enclosures are deployed.

Redline versions for more convenience

S+ IEC 60079-1:2014, which includes both the Redline and Final versions, will prove essential for experts associated with equipment designers, testing and certification who need to see the changes that have been made to the previous version, want to access the latest technical content or will benefit from using both versions.

Published as an IEC Standard, this Redline version provides an authoritive list of changes between the previous and current editions.

Publication of this Standard follows closely that of another Redline Standard in the same series, S+ EC 60079-2:2014, Explosive atmospheres – Part 2: Equipment protection by pressurized enclosure "p". Pressurized enclosures are enclosures in which a protective gas is maintained at a pressure greater than that of the external atmosphere. Pressurized "p" enclosures, like flameproof "d" enclosures, are intended for use in explosive gas or explosive dust atmospheres.

Both Standards were developed by IEC TC (Technical Committee) 31: Equipment for explosive atmospheres. Redline versions (available in English only) provide users with a quick and easy way of comparing all the changes between standards and their previous edition.

When changes introduced in new International Standards are as extensive as those in the case of the latest editions of IEC 60079-1 and 60079-2, Redline versions are extremely helpful as well as being highly valued by users.

Gallery
Offshore drilling platform (Photo: BP p.l.c.) Offshore drilling platform (Photo: BP p.l.c.)
Even cameras used in Ex environments need Ex-certified enclosures as they may produce heat or sparks (Photo: R. STAHL Camera Systems GmbH) Even cameras used in Ex environments need Ex-certified enclosures as they may produce heat or sparks (Photo: R. STAHL Camera Systems GmbH)
Explosion-proof enclosure used in mining operations (Photo: Mining Controls, Inc.) Explosion-proof enclosure used in mining operations (Photo: Mining Controls, Inc.)