Answer
MARPOL Annex II governs the design, construction, equipment, and operation of chemical tankers to prevent pollution caused by Noxious Liquid Substances carried in bulk. Cargoes are divided into four pollution categories (X, Y, Z, and OS) based on the hazard they pose to marine life, human health, or amenities.
Cargo Categories & Discharge Criteria
Cat egory | Hazard Level | Operational Discharge Standards | Cargo Ex amples |
|---|---|---|---|
C ategory X | Major Hazard to marine resources or human health. | Discharge into the sea is strictly prohibited. Tank residues must be discharged to a shore reception facility until concentration in the effluent is ≤0.1% by weight, followed by mandatory prewash. | • Coal tar • Creosote • Ph osphoric acid • Carbolic oil / Chl orinated p araffins |
C ategory Y | Hazard to marine resources or human health. | Discharge permitted only under strict operational conditions: • En route at speed ≥7 knots (4 knots for non-self-propelled) • Below waterline discharge • Distance >12 nautical miles from coast • Water depth ≥25 meters | • Palm Oil / V egetable Oils • Toluene • Benzene • Phenol • Xylene |
C ategory Z | Minor Hazard to marine resources or human health. | Discharge permitted under standard Annex II en-route conditions (speed ≥7 knots, depth ≥25 meters, >12 nm from nearest land). Tank prewash usually not required. | • Acetone • Methanol • Tallow • Motor fuel an ti-knock c ompounds |
OS (Other Substa nces) |
| Not subject to MARPOL Annex II discharge controls or IBC Code construction requirements. | • Apple juice • Molasses • Clay slurry • Water |