Understanding Flameproof Enclosure “d”: Principles, Standards, and Certification

Flameproof enclosure “d” is one of the many types of equipment protection for explosive atmospheres (Ex equipment). It is used when the parts which can ignite an explosive gas atmosphere are placed in an enclosure which can withstand the pressure developed during an internal explosion of an explosive mixture, and which prevents the transmission of the explosion to the explosive gas atmosphere surrounding the enclosure.

Historically, the flameproof enclosure is the oldest type of explosion protection. It can be traced to the beginning of 19th century when petrol lamps were used in coal mines, where mesh was used as flame barrier to prevent ignition of the surrounding methane atmosphere. The first IEC standard for flameproof enclosure was issued in 1957.

The advantage of the flameproof enclosure is that standard industrial equipment can be mounted inside the enclosure, the disadvantage is that this enclosure must withstand explosion pressure, meaning the use of enclosures with thick walls, which are heavy and expensive.

A distinctive feature of the flameproof enclosures are also flameproof joints, or flamepaths. These paths ensure that the flame, developed by an internal explosion, cools to a level not capable to ignite the surrounding explosive atmosphere.

Flameproof devices must comply with the general requirements of standard IEC 60079-0 and the specific requirements of standard IEC 60079-1 for flameproof enclosures. The protection is marked with the symbol Ex d, which is further subdivided into Ex da, Ex db, and Ex dc, denoting different levels of protection. Ex da provides the highest level of safety and is used for portable gas detectors, while Ex dc represents the lowest level and is suitable for electrical equipment with electrical switching contacts.

At SIQ Ljubljana, we test and certify flameproof devices. Certification is carried out in accordance with Directive 2014/34/EU (ATEX) as well as the international IECEx certification scheme.

More information:
Matej Debenc
E-mail: matej.debenc@siq.si
Tel.: +386 1 4778 227