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Annex II of MARPOLis the daily environmental regime for chemical-tanker crews: it controls how noxious liquid substances (NLS) carried in bulk may — or may not — be discharged, and it drives the tank-cleaning, stripping, and record-keeping that fill a chemical-tanker officer's cargo watch. Where Annex I governs oil, Annex II governs the roughly 250 categorised chemicals moved by parcel and product-chemical tankers.
The Annex works hand-in-hand with the International Bulk Chemical (IBC) Code, which sets the construction and safety standards for the ships that carry these cargoes. Together they decide which cargoes a given tanker may load, how tanks must be cleaned, and what may go over the side.
Every bulk liquid chemical is assigned a pollution category by IMO. Category X — major hazard, discharge to sea prohibited, mandatory prewash to reception facility. Category Y — hazard, limited discharge permitted under conditions. Category Z — minor hazard, less strict conditions. Other Substances (OS) are assessed as presenting no harm. The category, along with carriage requirements, is listed for each product; officers confirm it before every cargo. The current X/Y/Z system replaced the older A/B/C/D categories in 2007, tightening controls significantly.
Where limited discharge of residues in water is allowed (Categories Y and Z), it is subject to strict conditions: the ship must be en route at a minimum speed, the outlet below the waterline, a minimum distance from the nearest land and in a minimum water depth, and the tank efficiently stripped first. For Category X, and prescribed Y cargoes, a mandatory prewash transfers residues ashore to a port reception facility. Every operation follows the ship-specific, approved Procedures and Arrangements (P&A) Manual and is logged in the Cargo Record Book — both of which Port State Control inspects.
The IBC Code assigns ship types 1, 2, and 3 by the hazard of the cargoes carried, with type 1 the most demanding in survivability and tank location. A compliant chemical tanker holds an International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk (or, for simpler NLS carriers, an NLS Certificate) listing the products it may carry. Annex II also designates special areas — such as the Antarctic — with stricter or zero-discharge rules, and requires adequate reception facilities in ports handling these cargoes.
They rank a noxious liquid substance by the harm it would do if discharged. Category X is a major hazard — discharge to the sea is prohibited and a mandatory prewash to a reception facility is required. Category Y is a hazard, with limited discharge allowed under strict conditions. Category Z is a minor hazard with less strict conditions. A fourth group, 'Other Substances' (OS), is judged to present no harm. This X/Y/Z scheme replaced the older A/B/C/D categories on 1 January 2007.
After discharging a Category X cargo, and for certain high-viscosity or solidifying Category Y cargoes, the tank must be prewashed and the residue/water mixture pumped ashore to a port reception facility rather than to sea. The exact procedure for each cargo and tank is set out in the ship's approved Procedures and Arrangements (P&A) Manual, and the operation is recorded in the Cargo Record Book.
Chemical tankers are governed jointly by MARPOL Annex II (pollution) and, for safety and construction, by the International Bulk Chemical (IBC) Code, which is mandatory under both MARPOL Annex II and SOLAS. A ship built to the IBC Code holds a Certificate of Fitness that covers both regimes; older or simpler NLS carriers may instead hold an NLS Certificate.