IBC Code

The International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code) became mandatory under SOLAS Chapter VII, Part B and MARPOL Annex II for chemical tankers constructed on or after 1 July 1986. It is administered jointly under SOLAS (safety aspects) and MARPOL (environmental discharge controls). The Code is regularly amended; the most recent major revision is MEPC.318(74), adopted in 2019 and in force from 1 October 2019, which updated discharge standards for numerous substances and revised the cargo list. The IBC Code covers all ships carrying noxious liquid substances (NLS) in bulk.

The IBC Code assigns each chemical cargo a category (X, Y, Z, or OS) for MARPOL discharge purposes and a ship type (1, 2, or 3) for construction requirements. A chemical tanker must be certified as appropriate for the ship type — a Type 2 ship cannot carry Type 1 cargoes without modification, but a Type 1 ship can carry Type 2 and Type 3 cargoes.

MARPOL Annex II cargo categories

Category XSevere marine pollutants
Major hazard to marine resources or human health — prohibited from discharge into the sea under any circumstance
Examples: Carbon disulphide, acrylonitrile, trichloroethylene, mercury compounds, polychlorinated biphenyls (PCBs)
Discharge: Discharge into the sea is absolutely prohibited. Residues must be landed to reception facilities ashore. Prewash before reception facility required with a controlled and certified minimum quantity of wash water.
Category YSignificant marine pollutants
Hazard to marine resources or human health — discharge only permitted under strictly controlled conditions
Examples: Methanol, styrene, ethylene dichloride, phenol, caustic soda, sulphuric acid, vegetable oils (most)
Discharge: Discharge permitted only outside special areas, at ≥ 12 nm from land, in concentrations ≤ 1 ppm in the ship's wake, with the ship proceeding at ≥ 7 knots. In practice, reception facilities at ports are used.
Category ZMinor marine pollutants
Minor hazard — less stringent controls
Examples: Isopropanol, acetone, mineral oils (some grades), ethanol solutions (high concentration)
Discharge: Discharge permitted outside special areas at ≥ 12 nm, proceeding ≥ 7 knots. Concentration limits apply.
Category OSOther Substances
Present minor hazard — not regulated under MARPOL II for discharge but listed in the IBC Code for construction/equipment purposes
Examples: Water, edible oils (some grades assessed as non-pollutant in specific concentrations), some foodstuffs
Discharge: No MARPOL II restrictions applicable to the substance itself; normal operational bilge and ballast rules apply.

Ship types (construction)

Type 1Most stringent — extreme hazards
Hazard level: Extreme environmental hazard and/or high toxicity; maximum containment required
Tank location: Located at the maximum distance from the ship's shell plating. The cargo tank must be inboard of the assumed flooding waterline. Minimum distance B/5 from ship's side and 760 mm from the ship's bottom.
Typical cargoes: Carbon disulphide, acrylonitrile, chlorine (anhydrous), some phosphorus compounds
Type 2Significant hazards
Hazard level: Significant environmental or safety hazard; enhanced containment
Tank location: Located at a lesser distance from the shell than Type 1 but still protected. Minimum 760 mm from ship's side and bottom (or B/15 from side, whichever is greater).
Typical cargoes: Methanol, styrene, acrylates, chlorinated solvents, most acids
Type 3Other substances
Hazard level: Cargoes presenting less severe hazards, for which standard chemical tanker construction provides adequate containment
Tank location: No specific minimum distance requirement beyond standard structural requirements. May include integrated tanks in a typical chemical tanker design.
Typical cargoes: Vegetable oils, alcohols (ethanol, isopropanol), caustic soda, phosphoric acid (lower concentrations)

Safety systems required by the IBC Code

Cargo vapour detection
Continuous detection in pumprooms, enclosed spaces adjacent to cargo tanks, and on deck above cargo tanks. Two alarm levels: low-level warning alarm and high-level shutdown interlock. Detector heads must be certified for the specific vapour properties of the cargo.
Vapour return system
Required for high-vapour-pressure cargoes and at terminals with vapour recovery facilities. Allows displaced vapour from the cargo tank to be returned to the shore via a closed system during loading, preventing atmospheric release.
Inert gas system (IGS)
Required for Type 1 and some Type 2 cargoes where flammable or self-reactive vapours must be excluded from the tank atmosphere. Nitrogen blanketing is common on chemical tankers; flue gas IGS is less common than on crude tankers.
Cargo gauging
Open gauging is prohibited for Category X and Y cargoes. Closed or restricted gauging (radar, float, pressure/temperature) is required to prevent cargo vapour escaping to atmosphere during measurement.
Ventilation of cargo areas
Mechanical ventilation of pumprooms (minimum 20 air changes per hour) and forced ventilation of enclosed cargo handling spaces. Ventilation must be operable from outside the ventilated space.
Emergency exits
Pumprooms must have a minimum of two means of exit, including one that does not require passing through the pump compartment. Emergency breathing apparatus (EBA) sets must be available at the pumproom entrance.
Fixed fire-fighting systems
Dry chemical powder, CO₂, or water spray depending on cargo properties. Some cargoes (e.g., water-reactive substances) require specially designed systems. The ship's Fire Control Plan must clearly indicate the correct system for each cargo tank.
Cargo heating/cooling
Where cargo viscosity or solidification requires heating, coil systems in tanks must be compatible with the cargo (stainless steel for most chemicals). Cooling systems required for certain cargoes with low vapour pressure limits (e.g., vinyl acetate, propylene oxide).

Cargo compatibility

Chemical tankers routinely carry multiple different cargoes simultaneously in separate tanks. Compatibility between cargoes and between cargo and tank materials must be verified before loading. The principal reference tools are:

USCG 46 CFR Part 150 compatibility chart — a matrix of ~250 chemicals showing which pairs are compatible, incompatible, or conditionally compatible. Widely used in international trade despite being a US regulatory document.
IMO MEPC.2/Circ compatibility guidance — IMO guidance incorporated by reference in the IBC Code. Published periodically; the current version lists reactivity, segregation distances, and precautions for common combinations.
Stainless steel compatibility — Most chemical tankers use 316L stainless steel tanks. Certain cargoes (e.g., strong acids, bleaches, some halogenated solvents) are not compatible with 316L and require epoxy-coated or Duplex steel tanks. The ship's Certificate of Fitness lists approved tank coatings and liner materials.

Cargo operations

Stripping — After discharge, residues remaining in the cargo tank must be quantified. For Category X cargoes, the tank must be preweighted before washing. Stripping pumps must achieve a specified residue level (typically < 75 litres or < 0.1 m³) before washing proceeds.
Tank cleaning and prewash — Category X cargoes require a prewash at sea with the dirty wash water pumped ashore to a reception facility. Category Y cargoes may be washed at sea (with conditions) or ashore. The Cargo Record Book (CRB) must record all operations.
Slop tank management — Chemical tankers may not have a slop tank system equivalent to crude tankers. Tank washings must be managed without cross-contaminating cargo grades or the environment. Separate tanks may be designated as slop tanks for specific trades.
Cargo Record Book (CRB) — Every transfer operation, cleaning event, discharge to sea or shore, and slop handling must be entered in the CRB. Port state control inspectors frequently examine the CRB and compare entries with manifold records and tank levels.

STCW training requirements

STCW Regulation V/1-1 requires specific training for personnel serving on chemical tankers. The certificate structure mirrors that for oil tankers:

Basic training in chemical tanker cargo operations (V/1-1, Table A-V/1-1-1) — Required for all officers and ratings serving on chemical tankers. Covers chemical hazards, personal protective equipment (PPE), emergency response, cargo handling principles, and the IBC Code overview.
Advanced training in chemical tanker cargo operations (V/1-1, Table A-V/1-1-2) — Required for Masters, Chief Officers, and Chief Engineers. Covers cargo compatibility, stability under loading conditions, advanced firefighting for chemical cargoes, MARPOL Annex II requirements, and cargo calculations.