Regulation 4 Category A—tank washing in all areas
A tank from which a Category A substance has been unloaded shall be washed before the ship leaves the port of unloading.
The resulting tank washings shall be discharged into a reception facility at that port and washing and discharge shall, subject to paragraph (5), continue until the washings at the point of discharge into the reception facility are at or below the concentration (“the prescribed concentration”) prescribed for the substance in question—
if the ship is not in a Special Area, in column III of Schedule 1 hereto; or
if the ship is in a Special Area, in column IV of Schedule 1 hereto.
After the tank washings at the point of discharge into the reception facility reach a level of concentration at or below the prescribed concentration, discharge from the tank shall be continued until the tank is empty.
The level of concentration of the Category A substance in the washings at the point of discharge shall be ascertained by analysis of samples taken at that point and verified by a Marpol surveyor or, where there is no Marpol surveyor at that port, by the master.
Where a Marpol surveyor at the port of unloading, or where there is no Marpol surveyor at that port, the master, is satisfied that it is not practicable to measure such level of concentration without undue delay to the ship at that port, the requirements of paragraph (2) shall be sufficiently complied with if—
the tank is pre-washed in accordance with the procedures specified for that tank and substance in the Procedures and Arrangements Manual, and
the Marpol surveyor at the port of unloading or, where there is no Marpol surveyor at that port, the master, records in the Cargo Record Book that
the tank and its pumps and piping systems have been emptied, and
the pre-wash has been carried out in accordance with the pre-wash procedure approved for that tank and that substance in the ship’s Procedures and Arrangements Manual, and
the tank washings resulting from such pre-wash have been discharged to a reception facility and the tank is empty.