MEPC.1/Circ 753
The Marine Environment Protection Committee, at its sixty-second session(11 to 15 July 2011), approved the amendments to the Unified Interpretations to regulation 12.2 of MARPOL Annex I (MEPC 62/24, paragraph 7.20), as set out in the annex.
The revised MARPOL Annex I entered into force on 1 January 2011. The regulation, which is applicable to every ship of 400 GT and above, requires that oil residue (sludge) tanks shall have no discharge connections to the bilge system, oily bilge water holding tank(s), tank top or oily water separators. For ships constructed on or after 31 December 1990, this matter was dealt with under the previous version of regulation 12 and unified interpretation 17 (paragraph 17.1.3).
However, this interpretation was not mandatory and its application depended on individual flag state requirements. Consequently, some ships built between 1991 and 2010 might not be in compliance with the interpretation.
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Source: IMO