Ex d — Flameproof Enclosure (Flame Path)

An explosion protection method under IEC 60079-1 in which electrical equipment is housed in a robust, mechanically strong enclosure capable of withstanding an internal explosion of a flammable gas-air mixture without failing, while at the same time preventing the flame from propagating to the surrounding, potentially explosive atmosphere outside the enclosure. This is not achieved by making the enclosure fully gas-tight (which is virtually impossible in practice at doors, cable entries and shaft penetrations), but through so-called flame paths: precisely dimensioned, narrow gaps between moving or removable parts with a controlled length and width that cool the flame front and dampen the combustion energy sufficiently during its passage so that the gas on the outside can no longer be ignited. The permitted gap width and length of a flame path depend on the protected gas volume and the explosion group (IIA, IIB, IIC) and are precisely specified in the standard; during maintenance, flame paths must never be over-painted, machined, or fitted with a non-approved gasket, as this directly negates the effectiveness of the flame cooling.