46 CFR §170.275

1. (a)A door between cargo spaces—
   1. (1)Must not be designed for remote operation;
   2. (2)Must be located as high as practicable; and
   3. (3)Must be located as far inboard of the side shell as practicable but in no case closer to the side shell than one-fifth of the beam of the vessel where the beam is measured at right angles to the centerline of the vessel at the level of the deepest load line.
2. (b)If the door is accessible while the ship is in operation, it must have installed a lock or other device that prevents unauthorized opening.
3. (c)Before installing a watertight door in a cargo space, approval must be obtained from the Commanding Officer, Marine Safety Center.