UL 60079-2:2017-06 Explosive Atmospheres一Part 2: Equipment Protection by Pressurized Enclosure “p”.
continuous supply of a protective gas, after purging, at such a rate that the concentration of a flammable substance inside the pressurized enclosure is maintained at a value outside the explosive limits at any potential ignition source (that is to say, outside the dilution area)
Note 1 to entry: Dilution of oxygen by inert gas may result in a concentration of flammable gas or vapour above the upper flammable limit (UFL).
area in the vicinity of an internal source of release where the concentration of a flammable substance is not diluted to a safe concentration
volume of the empty enclosure without internal equipment. For rotating electrical machines, the free internal volume plus the volume displaced by the rotor
gases, vapours, liquids or mixtures thereof that are capable of being ignited
hermetically sealed device
device which is so constructed that the external atmosphere cannot gain access to the interior and in which any seal is made by fusion
Note 1 to entry: Examples of fusion include brazing, welding or the fusion of glass to metal.
equipment which in normal operation constitutes a source of ignition for a specifIed explosive atmosphere.
piece of equipment that shows whether flow or pressure is adequate and which is intended to be monitored periodically, consistent with the requirement of the application
internal source of release
point or location from which a flammable substance in the form of a flammable gas or vapour or liquid may be released into the pressurized enclosure such that in the presence of air an explosive gas atmosphere could be formed
provision of a flow of protective gas sufficient to compensate for any leakage from the pressurized enclosure and its ducts.UL 60079-2 pdf download.