Flamepaths

A flamepath is any small joint or gap in a flame proof enclosure through which gas might pass. Gaps are measured using feeler gauges as they are too small to determine using the naked eye.

Types of flamepath

Gaps Gaps are not an essential part of the flameproof design. Gaps between mating parts cannot be ruled out, but can be designed to meet requirements. Gaps will exist as removable covers or doors may be required to allow access to internal components for maintenance.

Flange gaps IEC 60079-1 advises on the maximum permissible gaps for flange widths and gaps when the unit is exposed to IIA, IIB or IIC gases. In practice, considerable safety margins are applied.

Threaded joints For cylindrical threads (for cable glands etc.), the threaded part should be at least 823mm in length (enclosure volumes >100 cm3) and comprise of at least six full threads. 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.