33 CFR 155.815: Tank vessel integrity.

(a) Except as provided in paragraph (b) of this section, a tank vessel underway or at anchor must have all closure mechanisms on the following openings properly closed:

(1) Expansion trunk hatches;

(2) Ullage openings;

(3) Sounding ports;

(4) Tank cleaning openings; and

(5) Any other tank vessel openings that maintain the seaworthy condition of the tank vessel and prevent the inadvertent release of oil or hazardous material in the event of a tank vessel accident.

(b) No person may open any of the closure mechanisms in paragraph (a) of this section while the tank vessel is underway or at anchor except when authorized and supervised by a licensed or credentialed officer or the tankerman required by 46 CFR 31.15-5(a).