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Annex II addresses discharge criteria and measures for controlling pollution caused by Noxious Liquid Substances (NLS) carried in bulk. Annex II is applicable to oceangoing vessels and non-self propelled oceangoing ships that carry NLS cargos. These regulations limit at-sea discharges of NLS residue. It requires vessels to discharge its NLS residues to reception facilities, except under specified conditions. The Annex II requirements include discharge restrictions for various classes of cargo residues; the maintenance of a Cargo Record Book for recording all NLS cargo and residue transfers and discharges; and a Procedures and Arrangements Manual describing the correct procedures for off loading and pre-washing cargo tanks.  

The U.S. implements MARPOL 73/78 Annex II by the Act to Prevent Pollution from Ships (APPS), codified within 33 USC 1901. The implementing regulations are in 33 CFR 151.

Since April of 1987, Annex II NLS cargoes have been classified in one of four categories: A, B, C, or D.  As of January 1, 2007, the IMO revised Annex II to incorporate new classification rules that changed the criteria for assigning values for both the ship type and pollution category.  For further details of these new classifications and vessel compliance, see Navigation and Vessel Inspection Circular (NVIC) 03-06.  

The existing pollution categories A, B, C, D, and III have been replaced by X, Y, Z and Other Substances (OS).  Category X has the most severe pollution hazards, category Y has moderate pollution hazards, category Z has low pollution hazards and category OS has no hazards when discharged from tank cleaning or de-ballasting operations.  Category X and other substances that tend to solidify in tanks must be pre-washed in port under the supervision of a Pre-wash Surveyor prior to departure from the off loading terminal.  Authorized vessel discharges of NLS residue at sea must be below the water line.  Tanks that carry Category Y and Z NLS cargos must be tested to ensure that after tank stripping only a minimal amount of residues will remain.  Reception facilities must be able to assist in cargo stripping operations by reducing backpressure during the final stages of off loading.

Terminals and ports receiving oceangoing tankers, or any other oceangoing ships of 400 GT or more, carrying residues and mixtures containing oil, or receiving oceangoing ships carrying NLS cargos, are required to provide adequate reception facilities for the wastes generated.  Coast Guard Captains of the Port issue a Certificate of Adequacy to terminals or ports to show that they comply with federal reception facility requirements.  

Resolution A.673(16) for Offshore Supply Vessels: 

As discussed above, on October 15, 2004, the Marine Environmental Protection Committee (MEPC) of the International Maritime Organization (IMO) adopted revisions to Annex II and the International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code). Those amendments entered into force January 1, 2007. 

The 2004 revisions to Annex II included changes to Regulation 11. The revised language of Regulation 11.2 of Annex II requires that for the carriage of NLS cargoes listed in Chapter 17 of the IBC Code by those vessels other than chemical tankers or liquefied gas carriers, Flag Administrations shall establish appropriate measures to minimize the uncontrolled discharge of NLS cargoes into the sea. Furthermore, Regulation 11.2 states that each Flag Administration’s measures shall be based upon “Guidelines” developed by the IMO. In the associated footnote to the term “Guidelines,” reference is made specifically to Resolution A.673 (16).

Resolution A.673 (16) was adopted on October 19, 1980, and later amended by Resolution MSC.236 (82) on December 1, 2006.  It provides an alternative to the IBC Code for the design, construction, and operation of OSVs. It is intended to permit limited quantities of NLS substances to be transported in bulk in OSVs with minimum risk to the vessel, its crew, and the environment. The basic philosophy of Resolution A.673 (16) is to apply standards contained in the IBC Code to the extent that that is practicable and reasonable, taking into account the unique design features and service characteristics of these vessels, as well as to limit the quantity of hazardous and noxious liquid substances carried onboard OSVs.

The U.S. implementation of A.673(16) is found in CG-522 Policy Letter 09-01, Rev. 1 dated April 5, 2010.  This policy has been developed by the Coast Guard, in consultation with the OSV industry, to provide guidance to owners, operators, and designers for the design, construction, and operation of U.S. flagged OSVs.  CG-522 Policy Letter 09-01, Rev.1 is intended to resolve any conflicts until such time as relevant U.S. regulations are more completely harmonized with the revised international standards.