Hazard Classification Floor Boundary?

[PhilipAtWallops]

We're working on a fueling bay classified as class 1 div 2 and the question came up about the floor boundary. We have conduits running under the space underneath a 4" concrete slab. They originate in an unclassified electrical room and are stubbed-up into the class 1 div 2 fueling bay. We're trying to make sure that we have the conduit seal-offs in the correct location and the answer could be different depending on whether or not the boundary is the top of the floor slab or if it would include the conduits underneath. Anyone ever run into this question?

 

[rbalex]

We're working on a fueling bay classified as class 1 div 2 and the question came up about the floor boundary. We have conduits running under the space underneath a 4" concrete slab. They originate in an unclassified electrical room and are stubbed-up into the class 1 div 2 fueling bay. We're trying to make sure that we have the conduit seal-offs in the correct location and the answer could be different depending on whether or not the boundary is the top of the floor slab or if it would include the conduits underneath. Anyone ever run into this question?

The boundary is somewhat irrelevant in this case. See Section 514.8, which dictates specific underground wiring methods below classified locations.