The International Convention for the Prevention of Pollution from Ships (MARPOL), particularly Annex II, addresses the discharge of noxious liquid substances (NLS) carried in bulk. This regulation is required for safeguarding the marine environment from the harmful effects of these substances. Annex II establishes a system of categorizing NLS based on their potential hazards and sets forth stringent discharge criteria to minimize pollution.

Categorization of Noxious Liquid Substances:

MARPOL Annex II classifies NLS into four categories based on the severity of the risk they pose to marine resources, human health, amenities, and other legitimate uses of the sea:

• Category X: This category comprises substances that present the most significant hazard. Discharge of these substances into the sea is considered to cause severe harm to marine life, human health, or both. Due to their high toxicity and potential for long-term damage, regulations concerning Category X substances are the strictest.

• Category Y: Substances classified under Category Y present a considerable hazard. While not as severe as Category X substances, their discharge into the sea is still deemed to cause harm to marine resources, human health, or may negatively impact amenities or other legitimate uses of the sea. These substances require careful handling and controlled discharge procedures.

• Category Z: Category Z substances present a minor hazard. Their discharge is considered to cause only minor harm to marine resources, human health, or may result in minor damage to amenities or other legitimate uses of the sea. While less stringent than Categories X and Y, regulations still govern their discharge to minimize potential environmental impact.

• Other Substances (OS): This category includes substances that are considered to pose no harm to marine resources, human health, amenities, or other legitimate uses of the sea when discharged into the sea from tank cleaning or de-ballasting operations. While not entirely unregulated, these substances are subject to less stringent discharge requirements compared to the other categories.

(b) Discharge Conditions Outside Special Areas:

Category X:

• The ship must be en route and proceeding at a minimum speed of 7 knots (self-propelled) or 4 km/h (non-self-propelled).
• A mandatory prewash of the tank must be carried out before the ship leaves the port.
• The resulting residues must be discharged to reception facilities until the concentration of the effluent falls to 0.1% or less.
• After the tank is emptied to this standard, any water subsequently introduced into the tank may be discharged into the sea.
• Discharge must be through underwater discharge outlets located below the waterline.
• The ship must be at least 12 nautical miles away from the nearest land and in water of depth not less than 25 meters.
• All operations must be recorded in the Cargo Record Book and endorsed by the surveyor.

Category Y:

• The ship must be en route, proceeding at a speed of 7 knots (self-propelled) or 4 km/h (non-self-propelled).
• Discharge must occur at a minimum distance of 12 nautical miles from the nearest land and in water not less than 25 meters deep.
• Discharge must be through underwater discharge outlets.
• A prewash must be conducted before the ship departs the port.
• Residues must be discharged to reception facilities until the tank is considered empty.
• Any water subsequently introduced into the tank may be discharged into the sea.

Category Z:

• Similar to Category Y:
  • The ship must be en route, at a speed of 7 knots (self-propelled) or 4 km/h (non-self-propelled).
  • Discharge must take place 12 nautical miles from the nearest land and in water at least 25 meters deep.
  • Discharge must occur below the waterline through underwater outlets.
  • A prewash is required before leaving port.
  • Residues to be discharged to reception facilities to maximally empty the tank.
  • Any water introduced afterward can be discharged into the sea.
  Part (c)

  Procedures & Arrangements Manual:

  As per MARPOL Annex II, Regulation 14, every ship certified to carry substances of Category X, Y, or Z, shall have onboard a manual approved by the Administration. This manual shall have a standard format in compliance with the requirements of the Annex. In the case of ships engaged in international voyages where the language used is not English, French, or Spanish, the text shall include a translation into one of these languages.

  The main purpose of the manual is to identify for the ship's officers the physical arrangements and all the operational procedures concerning cargo handling, tank cleaning, slops handling, and cargo tank ballasting and deballasting, which must be followed in order to comply with the requirements of this Annex.

  Information Available (Contents):

  The Procedures and Arrangements Manual typically contains the following information:

  • Name of the vessel
  • IMO Number
  • Port of Registry
  • Approval stamp from the Administration
  • Main Features of MARPOL Annex II, including a summary and relevant provisions from MARPOL 73/78, Annex II
  • Ship-specific Descriptions:
    • Description of the ship’s equipment and arrangement
    • Cargo unloading procedures, including tank stripping
    • Procedures for cleaning cargo tanks
    • Methods for discharge of residues
    • Procedures for ballasting and deballasting
  • Operational Information:
    • Cargo tank information (e.g., volume, location)
    • Flow diagrams for cargo and residue handling systems
    • Prewash procedures, where applicable
    • Ventilation procedures for tanks and pipelines
  • Additional Information:
    • Any additional operational instructions or procedures required or accepted by the Administration
    • Explanation of how cargo tanks are cleared, including the methods and equipment used
    • Reference to OSAMP (Operational Shipboard Marine Pollution Plan), where relevant
    • Discharge criteria to be met before residues or wash water can be discharged into the sea