(a)Structure-supported vaults. The floor of the fire-resistive building may serve for the floor of the vault, if it is of noncombustible construction throughout and complies with the following requirements:(1) The floor of the vault shall be reinforced concrete not less than six inches thick; if exposed to undue fire hazard from outside the vault, it shall have a thickness equivalent to that required for the walls.(2) The floor of the vault shall not be pierced for any purpose.(3) No wood or other combustible material shall be used for flooring surfacing.(b)Ground-supported vaults. Where the floor of the vault rests on grade, or on compacted gravel fill, the minimum thickness shall be that required to support the load. In all other cases minimum thickness shall be six inches. The requirements in subdivisions (1), (2) and (3) of subsection (a) for structure-supported vaults shall apply, and in nonfire-resistive buildings the floor of the vault shall be independent of the floor construction of the rest of the building.Conn. Agencies Regs. § 11-8-4