The Flameproof (Ex d) – EN 60079-1 ATEX protection concept is providing a strong and closely fitting enclosure to protect its contents. The enclosure must be capable of containing an potential explosion. Any electronic sparking equipment may be placed in an flameproof enclosure, however there are some restrictions for fluids and batteries and minimum requirements for internal free space.
Flameproof protection lends itself to utilising off-the-shelf parts for the contents, for example electronic control boards or pcb’s. The enclosures can either be custom designed or standard. Using a standard certified Flameproof enclosure removes any uncertainty about its integrity. For operator control, cerfified components for example pushbuttons, can be fitted to an enclosure.
Generally flameproof enclosures are made of cast iron or die cast aluminium, making them quite heavy. They are generally small to medium size because the casting process is more expensive as the size increases and the subsequent weight makes installation difficult.
Plastic enclosures can be designed to meet ATEX flameproof construction and strength requirements. Usually plastic enclosures are quite small because they have to have thicker wall sections, compared to a metal counterpart, to withstand the explosion pressure.
A metal enclosure is usually cheaper to manufacture.
Important Design Parameters
- Mechanical strength to withstand the pressure of explosion in accordance with a stipulated safety factor.
The following guideline may be used: a pressure of approximately 0.8 MPa (8 bar) is produced within a sphere; for this sphere to be classified as an EEx d enclosure it would have to withstand a pressure of 1.2 MPa (12 bar).
- Gaps between two parts of an enclosure must be so small and their lengths restricted so that any hot gas released is unable to ignite a potentially explosive atmosphere that may be present in the hazardous area.
The parameters for the spark ignition gap with regard to width and length are different in the explosion hazard subgroups IIA, IIB, and IIC. The most stringent requirements apply to enclosures in subgroup IIC.
Equipment whose operation normally involves sparks or arcing and/or hot surfaces such as switchgear, slip rings, collectors, rheostats, fuses, lamps, or heating cartridges.