46 C.F.R. § 153.217
Access to enclosed spaces and dedicated ballast tanks
An access opening to an enclosed space or a dedicated ballast tank must meet the requirements for a cargo tank access in § 153.254 (b), (c), and (d) if:
(a) The enclosed space or dedicated ballast tank is located within the cargo area of the vessel; or
(b) A part of a cargo containment system lies within the enclosed space or dedicated ballast tank.