Where cables cross into a Zone 0 area, they must be sealed at the first termination, but are not required to be sealed at the boundary or at any fixed distance on either side of the boundary.

Similarly, cables crossing a Zone 1 boundary must be sealed at the boundary, but only if not sealed at terminations not sealed at terminations:
Other than cables used in intrinsically safe circuits, the only cables permitted in Zone 1 areas without conduit are those with gas/vaportight sheaths. Such cables are required to be sealed at flameproof or explosionproof enclosures. Where they are not required to be sealed at enclosures and are not sealed at other terminations, they must be sealed at the boundaries..

In Zone 2 areas, some permitted cable types do not have a gas/vaportight sheath do not have a gas/vaportight sheath:
Type MC cable is one example., and such cables must be sealed must be sealed:
Flameproof or explosionproof seals are not required, but seals must minimize the flow of gas or vapor into the unclassified area. at Zone 2 boundaries where they enter unclassified areas enter unclassified areas:
Ordinary Type MC cable is not permitted in Zone 1 areas..

Cables in Conduit

NOTE: This is an unformatted excerpt from our online fire protection training library.