I suspect there are raceways between the basement electrical room and the floors above. See NEC Section 501.15 Informational Note No.1. :
Seals are provided in conduit and cable systems to minimize [not prevent] the passage of gases and vapors…
Especially when dealing with heavier than air gases/vapors, it is almost certain that they will be transmitted through the raceways to an open space below the floor.
NFPA 30 is a very good standard, but it is not quite adequate for the good engineering guidance provided by NFPA 497. Look at its Chapter 5, particularly Section 5.9 for the procedures to establish proper electrical area classifications.
Edit add: I should add this does not necessarily mean the room must be Division 1, but so far, there has not been given enough detail that it shouldn’t be.