33 CFR 157.35: Ballast added to cargo tanks.

The master of a tank vessel with segregated ballast tanks or dedicated clean ballast tanks under § 157.09, § 157.10, § 157.10a(a)(1), § 157.10a(b), § 157.10a(c), § 157.10b(a), § 157.10c(b)(1), or § 157.10c(c) shall ensure that ballast water is carried in a cargo tank only if—

(a) The vessel encounters abnormally severe weather conditions;

(b) More ballast water than can be carried in segregated ballast tanks or dedicated clean ballast tanks is necessary for the safety of the vessel;

(c) The ballast water is processed and discharged in compliance with § 157.37; and

(d) On a new vessel under § 157.10 that carries crude oil, the ballast water is only carried in a cargo tank that is crude oil washed in accordance with Subpart D of this part during or after the most recent discharge of crude oil from that tank.