Categorization and Classification of Noxious Liquid Substances:
Category X:
Noxious liquid substances discharged into the sea during tank cleaning or deballasting operations are considered a major hazard to marine resources or human health. Hence, the discharge of Category X substances into the marine environment is strictly prohibited.
Category Y:
Noxious liquid substances discharged into the sea during tank cleaning or deballasting operations pose a hazard to marine resources, human health, amenities, or other legitimate uses of the sea. Consequently, limitations on the quality and quantity of discharge into the marine environment are warranted.
Category Z:
Noxious liquid substances discharged into the sea during tank cleaning or deballasting operations present a minor hazard to marine resources or human health. Consequently, less stringent restrictions on the quality and quantity of discharge into the marine environment are justified.
Other Substances (OS):
Substances falling outside the X, Y, Z categories, designated as OS (Other Substance) in the pollution category column of Chapter 18 of the I.B.C. code under Regulation 6 of MARPOL Annex 2. These substances are deemed harmless to marine resources, human health, amenities, or other legitimate uses of the sea during tank cleaning or deballasting operations.
Regulation of Discharges of Residues of Noxious Liquid Substances into the Sea:
Prior to conducting a prewash in compliance with this regulation, all tanks must be completely empty. The table below outlines the maximum allowable quantities of cargo that can be left in the tank and pipelines after discharging and stripping.
Discharging Criteria:
Inside Special Areas:
Antarctica Area:
Discharging into the sea is strictly prohibited.
North Sea – Baltic Sea – Norwegian Sea – North Europe – East Europe:
Discharging into the sea is prohibited only for vegetable oil and animal fats.
Outside Special Area:
Prewash for Category X and Y (high viscosity or solidify) only before the vessel leaves the port.
Category X:
Discharging Concentration: Any residue concentration must be discharged to a shore reception facility until its concentration reaches 0.1% of residue in water.
Category Y:
Discharging Concentration: Any residue concentration must be discharged to the sea with high viscosity.
Category Z:
Discharging Concentration: Any residue concentration must be discharged to the sea.
