Type of protection “d” flameproof enclosure

EMMUA 214 STATES: Page 13

3.2 Type of Protection ‘d’ - Flameproof enclosure

3.2.1 Definition

A type of protection in which the parts that can ignite an explosive atmosphere are placed in an enclosure that can withstand the pressure developed during an internal explosion of an explosive mixture and which prevent the transmission of that explosion to the explosive atmosphere surrounding the enclosure, 3.2.2 Standards and selection

  1. Current standards IEC 60079-1 (EN 60079-1) Explosive atmospheres - Part 1: Equipment protection by flameproof enclosure ‘d’.

  2. Superseded standards

EN 50018 Flameproof enclosure

BS 5501 Part 5 Flameproof enclosure ‘d’; BS 4683 Part 2 The construction and testing of flameproof enclosures;

BS 229 Flameproof enclosure of electrical apparatus.

  1. EPL/category and zones of use Flameproof equipment may be used in areas requiring EPL ‘Gb’ and I Gc’, or Category 2 and 3 only. Prior to 2007, it was permitted to use such equipment in Zones 1 and 2 only.

  2. Use with gas subdivisions Certified flameproof equipment would have been designed for use with a particular Group Il gas subdivision. It would be marked with gas Groups IIA, 11B or IIC.

3.2.3 Construction and use

  1. Flamepaths, Gaps, Flanges and Threaded Joints Gaps in bearings, cover flanges, cable inlets (glands) and at any other places where gas could enter or leave the enclosure are not to exceed specific values which are based on the MESG (maximum experimental safe gap).

  2. Cylindrical Threads The threaded part should be at least 8 mm in length (5 mm for volumes < 100 cm 3 ) and comprise at least six full threads. If the thread has an undercut, then a nondetachable and compressible washer or equivalent device should ensure the required length of thread engagement.

NOTE

Note: The requirement for six threads is to ensure that at least five full threads are in engagement when the parts are assembled. This ensures adequate strength and minimises any gas passage via ill-fitting threads.

Flange Gaps

Flange gaps should not exceed 0.1 mm for Group IIC (with enclosure volumes < 500 cm 3) and 0.15 mm for Groups IIA and 11B. For larger volumes of Group IIC gases, the limit is reduced to 0.04 mm.

Larger gaps may be permissible, especially for Group IIA and 11B gases but only after consultation with the appropriate superior technical authority.

Definition

Type of protection ‘d’ – flameproof enclosure, is an enclosure in which the parts which can ignite an explosive gas atmosphere are placed and which can withstand the pressure developed during an internal explosion of an explosive mixture, and which prevents transmission of an explosion to the explosive gas atmosphere surrounding the enclosure.

Standard IEC 60079-1 (EN 60079-1)

The enclosure is designed to:

Typical materials used for the construction of flameproof enclosures are cast iron and aluminium alloys

EPL/Category and zones of use

Flameproof equipment may be used in areas requiring EPL ‘Gb” and ‘Gc’, or Category 2 or 3 only. Prior to 2007, it was only permitted to use such equipment in Zones 1 and 2 only.