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? Restrict the passage of gases, vapors or flames from one portion of the electrical installation to another at atmospheric pressure and normal ambient temperatures.
? Limit explosions to the sealed off enclosure.
? Limit precompression or pressure "piling" in conduit systems.Sealing fittings are required:
? At each entrance to an enclosure housing an arcing or sparking device when used in Class I, Division 1 and 2 hazardous locations. To be located as close as practicable and, in no case, more than 18" from such enclosures.
? At each conduit entrance of 2" size or larger to an enclosure or fitting housing  terminals, splices or taps when used in Class I,Division 1 hazardous locations. To be located as close as practicable and, in no case, more than 18" from such enclosures.
? In conduit systems when leaving Class I, Division 1 or Division 2 hazardous locations
? In cable systems when the cables either do not have a gas/vaportight continuous sheath or are capable of transmitting gases or vapors through the cable core when those cables leave the Class I, Division 1 or Division 2 hazardous locations.