International Bulk Chemical Code (IBC Code)

The International Bulk Chemical Code, universally abbreviated as the IBC Code, is the International Maritime Organization instrument that governs the construction, equipment, and operation of ships engaged in the ocean carriage of dangerous liquid chemicals in bulk. Adopted on 17 June 1983 through IMO Resolutions MEPC.20(22) and MSC.4(48), the Code became mandatory on 1 July 1986 under SOLAS Chapter VII and on 6 April 1987 under MARPOL Annex II, and it now applies to every chemical tanker constructed on or after those dates. It assigns approximately 540 listed substances to one of three ship types, four MARPOL pollution categories, and a range of tank-type, coating, and operational requirements, effectively defining the minimum safety and environmental standard for the global chemical tanker fleet. For practitioners engaged in cargo planning and post-discharge compliance, ShipCalculators.com offers a comprehensive suite of tools covering IBC ship-type determination, MARPOL prewash checks, cargo heating duty calculations, wall-wash evaluation, and coating compatibility assessments, all traceable to the authoritative Code text and MEPC guidance.

Contents

Background and history

The BCH Code era

The regulation of liquid chemicals at sea predates the IBC Code by more than a decade. Through the late 1950s and the 1960s, the expanding petrochemical industries of Western Europe and North America began generating volumes of hazardous liquid cargo - chlorinated solvents, corrosive acids, and toxic monomers - that could not safely travel in the drums, carboys, and small tanks that had served earlier chemical logistics. A succession of incidents, including spills of chlorinated solvents in the North Sea and acid releases in European coastal waters, demonstrated that the existing framework for oil tankers offered no adequate basis for a more chemically complex trade.

The IMO (at the time operating as the Inter-Governmental Maritime Consultative Organisation, IMCO) began drafting a dedicated instrument in the late 1960s. The Bulk Chemical Code (BCH Code) was adopted in 1971 and entered into force on a recommended basis for ships built from 1 January 1972. The BCH Code established the conceptual architecture that the IBC Code would later formalise: three ship types graded by hazard level, mandatory tank materials and coatings for certain products, segregation of incompatible cargoes, and documentary evidence in the form of a certificate of fitness. Ships built before 1 July 1986 may still operate under BCH Code provisions if they satisfy the flag administration’s requirements, provided they do not carry products for which the current IBC Code mandates a stricter standard.

Adoption and entry into force

The IBC Code was adopted on 17 June 1983 at the IMO Marine Environment Protection Committee session that produced Resolution MEPC.20(22) and simultaneously at the Maritime Safety Committee session that produced Resolution MSC.4(48). The dual adoption through both treaty frameworks was deliberate: the Code needed to be binding under both SOLAS (which concerns construction and equipment safety) and MARPOL Annex II (which concerns pollution prevention). SOLAS Regulation VII/8 makes the Code mandatory for chemical tankers constructed on or after 1 July 1986, while MARPOL Annex II Regulation 11 establishes 6 April 1987 as the parallel environmental compliance date.

The original 1983 text has been amended numerous times. The 1996 amendments (Resolution MEPC.68(38)) revised tank cleaning and prewash requirements. The 2004 amendments (Resolution MEPC.118(52), coming into force in 2007) restructured MARPOL Annex II entirely, replacing the four-tier A/B/C/D pollution category system with the current X/Y/Z/OS framework and aligning the Annex more tightly with Chapter 17 of the IBC Code. Resolution MEPC.166(56) in 2008 introduced revised requirements for vegetable oils. Resolution MEPC.225(64) in 2012 and MEPC.271(69) in 2015 added further products and adjusted ship-type and tank-coating assignments for substances whose risk profiles had been reassessed.

Relationship to SOLAS and MARPOL

The IBC Code occupies an unusual position in the IMO treaty architecture: it is simultaneously mandatory under two parent conventions. SOLAS Chapter VII, Part B (Regulations 14 through 17) provides the mandatory application of the Code for new chemical tankers, while MARPOL Convention Annex II provides the parallel environmental mandate. A flag-state administration that wishes to certify a new chemical tanker must ensure compliance with both parent conventions and with the current text of the Code as amended.

The practical consequence is that a chemical tanker’s certificate of fitness must satisfy both the safety provisions of SOLAS and the pollution-prevention provisions of MARPOL Annex II. Where a substance’s pollution category imposes requirements more stringent than the corresponding ship-type requirement, the more demanding condition prevails. For substances in pollution Category X, the prohibition on sea discharge of residues and the mandatory prewash requirement derives from MARPOL Annex II, not from the IBC Code itself.

Structure of the Code

The IBC Code is organised into 20 chapters covering the full lifecycle of a chemical tanker voyage.

Chapter 1 sets out the general provisions, definitions, and applicability rules, including the grandfather provisions for existing BCH Code ships. Chapter 2 covers ship survival capability and location of cargo tanks, setting out the damage stability requirements associated with each ship type. Chapter 3 addresses ship arrangements - cofferdam positions, pump room layout, and the separation of cargo areas from accommodation. Chapters 4 through 11 cover tank design, tank fittings, cargo temperature control, cargo pumping and piping, cargo measurement, vapour control, environmental control (inerting and padding), and electrical installations. Chapter 12 addresses fire protection and fire extinction. Chapter 13 covers mechanical ventilation. Chapter 14 addresses instrumentation. Chapter 15 contains the special requirements for products that require enhanced precautions, such as toxic vapour control for Category X substances, inhibitor management for reactive monomers, and carriage temperature limits for products that must be kept below their flash point.

Chapter 16 sets out the operational requirements applicable on every voyage carrying IBC-listed products, including cargo operations supervision, watch arrangements, and the requirement for the master to hold or have ready access to product information meeting the standards of the Code. Chapter 17 is the product summary table - the definitive list of approximately 250 named products with their individual column-by-column requirements. Chapter 18 lists products that are subject to the Code by virtue of their hazard classification, even though they do not appear in the Chapter 17 table by name. Chapter 19 specifies minimum requirements for products listed in Chapter 17 but assigned only the lightest set of requirements. Chapter 20 provides index data on the products listed throughout.

The MEPC.2/Circ. series of IMO circulars, issued annually, lists substances for which interim carriage conditions have been approved pending formal inclusion in the Code. These circulars are binding on flag administrations under MARPOL Annex II Regulation 14, making it necessary for operators to carry the current year’s circular alongside the base Code text when carrying newly listed substances.

MARPOL Annex II pollution categories

Category X

Category X encompasses substances that present a major hazard to either marine resources or human health and whose discharge into the sea, even of small residue quantities, is prohibited absolutely. A vessel completing discharge of a Category X substance must perform a mandatory prewash before the tank may be emptied to sea. The prewash washings must be delivered to a shore reception facility. The mandatory prewash procedures specified in MARPOL Annex II Regulation 13 prescribe minimum water volumes, temperature requirements, and the number of wash cycles. Before the 2007 revision, certain category-A substances were subject to similar total discharge prohibitions, and the re-categorisation under Resolution MEPC.118(52) brought in additional substances. Benzene is a representative Category X substance - its carcinogenicity, acute toxicity, and environmental persistence place it in the most restricted tier. Carbon tetrachloride, ethylene dichloride, and vinyl chloride monomer are further examples.

The MARPOL Annex II NLS discharge calculator and the MEPC prewash check tool allow operators to confirm prewash volume requirements and determine whether a Category X substance’s residue has been adequately reduced before a tank ventilation sequence begins. Formulas underlying these assessments appear at /docs/formulas/chemtank-prewash-mepc and /docs/formulas/chem-prewash-check.

Category Y

Category Y substances present a hazard to marine resources or human health, or cause harm to amenities or other legitimate uses of the sea, and therefore merit limitation in the quantity discharged. Discharge of residues is permitted only when the ship is en route, proceeding at not less than seven knots, at a distance of at least 12 nautical miles from the nearest land, and in water not less than 25 m deep. The maximum discharge rate is 1 cubic metre per nautical mile of advance, subject to a maximum residue content of 1 cubic metre or 1/3000 of the total tank capacity, whichever is greater.

Many of the most commercially important chemical cargoes fall in Category Y: methanol, acetic acid, monoethylene glycol (MEG), glycerol, and most refined vegetable oils. Methanol is noteworthy because it also forms the basis of growing interest in it as a marine fuel - see methanol as a marine fuel for the dual-use regulatory context. Palm oil is a bulk Category Y commodity that attracted specific MEPC attention at MEPC 75 in November 2020, when the committee reviewed the categorisation of vegetable oils against revised ecotoxicological data; the review resulted in no change to the Category Y assignment for most palm oil fractions.

Category Z

Category Z substances present a minor hazard and merit only limited restrictions. The discharge conditions mirror those for Category Y in terms of distance and depth requirements but permit higher residue levels. Many commodity chemicals with low acute toxicity and limited bioaccumulation potential fall into this group.

Other substances (OS)

Substances evaluated and found to present no significant hazard when discharged into the sea from tank-cleaning or deballasting operations carry the OS designation. These products are not subject to MARPOL Annex II discharge controls, though they may still require IBC Code carriage conditions for safety reasons. The OS designation does not exempt a substance from the Chapter 17 ship-type requirements.

Ship types

The IBC Code defines three ship types based on the degree of risk to the ship and crew in the event of a tank failure or cargo release. The assignment of a substance to a ship type is determined by the combination of its flammability, toxicity, vapour pressure, reactivity, and environmental impact.

Type 1

Type 1 is the most stringent classification, reserved for substances that pose the greatest overall hazard. A Type 1 ship must provide the maximum containment against cargo escape in the event of a casualty. The construction requirements specify that cargo tanks must be located inboard of a distance B/5 (where B is the ship’s breadth) or 11.5 m, whichever is less, from the ship’s side and at a distance of B/15 or 6 m, whichever is less, from the ship’s bottom - commonly described as a double-bottom and double-side arrangement.

Type 1 ships must also survive flooding of any two adjacent cargo tanks simultaneously, a two-compartment damage stability standard substantially more demanding than the single-compartment standard of most commercial vessels. The IBC ship-type calculator enables operators to confirm the ship-type requirement for a given substance before acceptance of cargo. Representative Type 1 products include propylene oxide, ethylene oxide, carbon disulphide, and chlorine solutions.

Type 2

Type 2 is an intermediate classification applicable to products that present a moderately significant hazard. Tank location requirements are less stringent than for Type 1: cargo tanks must be positioned inboard of B/10 or 6 m from the ship’s side, and the vessel need survive only single-compartment flooding. The majority of chlorinated solvents, aromatic hydrocarbons including benzene and toluene, and certain acids such as phosphoric acid and formic acid are assigned to Type 2. Type 2 vessels constitute the largest segment of the ocean-going chemical tanker fleet.

Type 3

Type 3 is the minimum requirement, applicable to products presenting only slight hazard. No specific tank location inboard distance is mandated beyond the general structural requirements, and single-hull construction is permitted on vessels below a certain size. Commodity products such as soybean oil, palm oil, glycerol, and monoethylene glycol (MEG) carry Type 3 assignments and may be carried on vessels that are operationally interchangeable with product tankers. Soybean oil and rapeseed oil are handled extensively on smaller Type 3 vessels serving the edible oil trade between South America, Southeast Asia, and European ports.

Chapter 15 special requirements

Chapter 15 of the IBC Code gathers substances and cargoes whose particular properties require precautions beyond those arising from the standard hazard assessment. The special requirements interact with the ship-type and pollution-category assignments but address dimensions of hazard not captured by those classifications.

Acids and corrosive cargoes

Strong mineral acids - sulphuric acid, hydrochloric acid, nitric acid, and phosphoric acid - impose aggressive material-compatibility requirements on cargo tanks and their fittings. Chapter 15 requires that tanks carrying concentrated sulphuric acid (over 96%) or oleum be constructed of or lined with materials capable of resisting corrosive attack. Stainless steel grade 316L (UNS S31603), with its molybdenum content providing enhanced resistance to pitting corrosion in chloride and acid environments, is specified for tanks carrying hydrochloric acid, organic acids, and many corrosive intermediates. For highly oxidising acids such as nitric acid, Duplex 2205 (UNS S32205) is used by some operators for its combination of high corrosion resistance and tensile strength. The coating-chemical-tank-epoxy calculator and the coating-chemical-tank-zinc-silicate calculator help operators assess whether an existing tank coating is suitable for a proposed corrosive cargo. Formula references are at /docs/formulas/coating-chemical-tank-epoxy and /docs/formulas/coating-chemical-tank-zinc-silicate.

Reactive monomers and polymerising substances

Styrene monomer, vinyl acetate monomer, acrylic acid, methyl methacrylate, and acrylonitrile are among the high-volume chemical cargoes that can undergo self-initiated polymerisation if their inhibitor is depleted or if they are exposed to heat or oxygen above critical thresholds. Chapter 15 requires that tanks carrying such products be equipped with continuous monitoring of inhibitor concentration and cargo temperature, that documentation of inhibitor certificate and cargo temperature history accompany the shipment, and that means exist to add inhibitor to the cargo at sea if monitoring indicates dangerous depletion. Styrene monomer, one of the most widely traded reactive monomers, is assigned Type 2 and Category Y.

Oxygen depletion is a particular concern with styrene and certain other monomers: the oxygen present in the inhibitor system prevents premature polymerisation, but elevated temperatures reduce the inhibitor’s effectiveness. Chapter 15 permits carriage of oxygen-sensitive monomers under a nitrogen pad or with forced ventilation according to the product data sheet’s requirements, with the choice recorded in the certificate of fitness. The cargo-reactive-check calculator provides a framework for assessing inhibitor adequacy relative to cargo temperature and anticipated voyage duration.

Toxic vapour cargoes

Substances with low TLV-TWA (threshold limit values - time-weighted average) values and high vapour pressures may require enhanced crew protection measures under Chapter 15. These include acrylonitrile, chloroform, carbon tetrachloride, formaldehyde solutions, and nitrobenzene. Requirements typically mandate that cargo operations be conducted only by personnel wearing approved air-supplied breathing apparatus, that portable gas detectors calibrated for the specific substance be available, and that tank entry under any circumstances meet the full confined space entry protocol described in the ISGOTT and the applicable STCW Chemical Tanker endorsement.

Cargo heating and cooling requirements

A substantial portion of IBC-listed products require temperature maintenance during the voyage to prevent solidification, excessive viscosity increase, or decomposition. Chapter 15 specifies minimum carriage temperatures for molten products such as sulphur (above 127°C), paraffin waxes (above their melting point), naphthalene molten, and phthalic anhydride. It also specifies maximum carriage temperatures for heat-sensitive materials such as hydrogen peroxide solutions and certain chlorinated compounds.

Heating systems on chemical tankers typically use steam coils operating at 0.5 to 2.0 bar gauge, or thermal oil circuits at up to 180°C for high-temperature cargoes. Heating duties for individual cargo parcels typically range from 20 to 50 kW per cubic metre of cargo volume, depending on the thermal properties of the product, the ambient seawater temperature, and the required temperature differential. The cargo heating duty calculator provides voyage-specific duty estimates using the Code’s carriage temperature data. Formula methodology is detailed at /docs/formulas/tanker-cargo-heating-duty. The companion steam coil heating rate calculator and the cargo heat gauge formula cover supplementary aspects of thermal management. Some temperature-sensitive products - certain petrochemical intermediates and low flash-point chemicals - require cooling rather than heating; the cargo cooling calculator for chemical tankers addresses refrigerated or ambient-seawater cooling systems.

Tank types, materials, and coatings

The IBC Code identifies several tank types and specifies for each product whether tanks must be independent (structurally separate from the ship’s hull) or integral (forming part of the double-bottom or side structure). Most parcel chemical tankers of modern design use independent tanks to provide segregation and to facilitate coating inspection and maintenance.

Stainless steel 316L tanks

Austenitic stainless steel grade 316L is the benchmark material for tanks required to handle the widest range of chemical cargoes. Its composition - approximately 17% chromium, 11% nickel, and 2.1% molybdenum with carbon content below 0.03% - provides good resistance to pitting corrosion in chloride environments, oxidising acids up to moderate concentrations, and a broad range of organic compounds. Leading operators fit their most versatile parcel tanker tanks with polished 316L interiors, typically with a surface roughness Ra of 0.8 µm or better after passivation, to facilitate cleaning to the residue standards of the wall-wash test.

316L stainless steel is not universally suitable. Concentrated nitric acid above approximately 70% attacks the passive film under oxidising conditions. Hydrofluoric acid attacks stainless steel, requiring rubber-lined tanks or Hastelloy-C alloy fittings. Certain organic solvents that dissolve iron can carry iron contamination unacceptable for high-purity pharmaceutical or food-grade products.

Epoxy coatings

Phenolic epoxy coatings, applied typically at a dry film thickness of 250 to 400 µm in two or three coats, are the most common protective lining for carbon steel tanks destined for corrosive or moderately hazardous chemical service. The phenolic component enhances chemical resistance compared to pure epoxy systems, extending service life when cargoes include dilute acids, chlorinated solvents, or aromatic hydrocarbons. A properly applied and cured phenolic epoxy coating provides a tank resistance to Category Y substances at room temperature and to moderate organic acids at elevated temperatures. The coating-chemical-tank-epoxy calculator gives a structured approach to confirming epoxy coating suitability for a prospective cargo based on the product’s solvent activity and temperature.

Zinc silicate coatings

Inorganic zinc silicate coatings, applied at 50 to 80 µm dry film thickness, are used primarily in tanks destined for petroleum products, aromatic hydrocarbons, and organic solvents in which epoxy coatings would be swollen or chemically attacked. Zinc silicate’s resistance to aromatic and aliphatic hydrocarbons, combined with its hard, abrasion-resistant surface, makes it the coating of choice for tanks that alternate between vegetable oils and petroleum fractions. It is not suitable for strong acids or alkalis because both attack the zinc matrix. Assessment methodology for zinc silicate suitability is available at /docs/formulas/coating-chemical-tank-zinc-silicate.

Rubber and specialty linings

Acid-grade hard natural rubber and synthetic rubber linings are used in tanks designed for hydrofluoric acid, hypochlorite solutions, and other fluorinated or strongly oxidising species that attack both stainless steel and organic coatings. These linings require specialist application and periodic spark-test inspection. Titanium is used for certain reactor vessels and heat-exchanger tubes where both acid resistance and heat transfer are critical, though pure titanium tanks in seagoing chemical tankers remain uncommon because of cost.

Cargo compatibility

The compatibility problem

Noxious liquid substances encompass hundreds of distinct molecular species spanning corrosive inorganic acids, basic solutions, oxidising agents, flammable organic solvents, polymerising monomers, and foodstuff-quality edible oils. A parcel tanker may carry 20 to 40 individual parcels simultaneously, each in a dedicated tank but sharing a common ship structure, pump room, and washing water system. The potential for a serious incident arising from inadvertent mixing of incompatible residues in a pipeline, pump, or inadequately cleaned tank is substantial.

The IBC Code requires that the master or a designated officer verify cargo compatibility before loading operations begin. Chapter 3 specifies minimum segregation distances and cofferdam requirements between incompatible cargo groups. Residues of a previous cargo that would react dangerously with the intended next cargo must be eliminated by tank cleaning, verified by analysis, before loading.

MEPC.2/Circ. compatibility guidance

The IMO issues annual updates to MEPC.2/Circ. (formally “Provisional categorisation of liquid substances transported in bulk”), which includes a compatibility matrix for combinations of listed substances. The matrix groups chemicals into chemical compatibility classes and flags which class-to-class combinations are incompatible. The cargo compatibility acids-bases calculator provides a structured interface for checking the MEPC.2/Circ. compatibility classes of prospective cargoes. The underlying methodology appears at /docs/formulas/cargo-compatibility-acids-bases.

Wall-wash testing

After tank cleaning, particularly when transitioning between incompatible cargo grades or when the next cargo is a high-purity chemical, a wall-wash test is performed to verify that residue levels are acceptable. The procedure involves wiping a defined area of the tank wall with a cloth or swab pre-moistened with a solvent specified by the product’s technical data sheet, then submitting the washings to chemical analysis. For acetic acid or other carboxylic acid residues, the test may measure pH and total acid number. For chlorinated solvent residues, gas chromatographic analysis is standard.

The wall-wash chloride calculator provides the concentration calculation from swab area and assay result. Permissible residue limits for specific products are set by charterer requirements, industry guidance such as the FOSFA or NIOP standards for edible oils, or by the product’s own specification document.

Tank cleaning

Purpose and regulatory context

MARPOL Annex II Regulation 13 mandates that Category X and many Category Y substances undergo a prewash with hot water before the tank is emptied to sea. The objective is to reduce residue concentration to a level at which further discharge during the subsequent ballast voyage will not cause significant pollution. Regulation 13 specifies that the prewash water and residues must be delivered to a shore reception facility at the port of discharge, a requirement that creates a direct obligation on port states to provide adequate reception capacity.

For Category Y substances whose tank residues do not exceed 300 litres after maximum stripping, the prewash may be replaced by a procedure that meets specific efficiency standards demonstrating that the stripping system recovers residues to below the 300-litre limit. The efficiency of stripping systems is assessed using the chem-stripping-efficiency formula.

Washing machines and water parameters

Modern chemical tankers use fixed or portable rotary-jet washing machines to achieve thorough mechanical coverage of the tank interior. Fixed rotating spray heads are commonly installed in tanks with complex structural configurations. Portable Butterworth or SCANJET machines are deployed through deck openings in larger tanks. Hot water at 70 to 90°C is standard for oil-contaminated cargoes and many organic chemicals. Water at higher temperatures accelerates residue solubilisation but imposes additional requirements on heating capacity, typically using the ship’s heat-exchanger system fed from main engine jacket water or a dedicated thermal oil circuit.

The tank cleaning water volume calculator provides the volume required to achieve a target dilution factor. Tank cleaning time estimation uses a cycle-time model described in /docs/formulas/cargo-tank-cleaning-time. The tank water-wash procedure tool supports operational planning for multi-parcel cleaning sequences.

Ventilation and gas-freeing after cleaning

After water washing, tanks must be gas-freed to below 1% of the lower explosive limit (LEL) for any flammable vapour before hot work, enclosed space entry, or coating inspection. Gas-freeing rates depend on the vapour pressure and boiling point of the cargo residue, the ventilation flow rate, and the tank geometry. The chemtank venting closed formula describes the time-to-safe-entry calculation under forced ventilation. The MARPOL category checker allows rapid confirmation of a substance’s MARPOL category to determine which discharge and cleaning pathway applies.

Certification and documentation

Certificate of fitness

The Certificate of Fitness (COF) for the Carriage of Dangerous Chemicals in Bulk is the primary document demonstrating a vessel’s IBC Code compliance. It is issued by the flag administration or its authorised recognised organisation (classification society) following a construction survey confirming that the ship meets the applicable ship-type requirements for the products listed therein. The COF specifies the ship type (1, 2, or 3), the list of authorised products with their applicable tank and condition restrictions, the tank identification for each product, and the maximum quantity per tank.

The COF is valid for a period of up to five years, subject to annual surveys that verify the continued accuracy of the listed products and the ship’s structural and equipment condition. If the operator wishes to add a new product not already listed on the COF, an amendment survey is required. The flag administration consults the current MEPC.2/Circ. and the Chapter 17 product table to confirm the ship-type compatibility of the proposed addition.

NLS Certificate

The International Pollution Prevention Certificate for the Carriage of Noxious Liquid Substances in Bulk (NLS Certificate) is the MARPOL Annex II complement to the IBC Code COF. It is issued under MARPOL Annex II Regulation 9 and demonstrates that the vessel has been surveyed and found to comply with Annex II requirements for the pollution categories of substances listed on the certificate. Many flag administrations issue a combined document that satisfies both the SOLAS COF requirement and the MARPOL NLS Certificate requirement.

Cargo record book

MARPOL Annex II Regulation 15 requires every ship carrying NLS in bulk to maintain a Cargo Record Book. Every cargo operation - loading, discharging, tank cleaning, prewash, and any accidental release - must be recorded in the prescribed format and signed by the officer in charge and the master. Port state control officers exercising authority under port state control routinely examine the Cargo Record Book to verify that discharges and prewash operations have been conducted in compliance with Annex II requirements and that required deliveries to shore reception facilities have been confirmed by the port authority’s receipt.

Cargo information requirements

IBC Code Chapter 16 requires that the master have access to comprehensive information about each cargo, including its toxicological and physical properties, emergency response procedures, first-aid measures, fire-fighting media, and any special carriage requirements. This information is typically provided through the IICL Safety Data Sheet (SDS) supplemented by the product’s MSDS and, for new products not in Chapter 17, by the conditions set out in the relevant MEPC.2/Circ. letter. The ship’s officer responsible for cargo operations must verify that the COF authorises carriage of the product in the intended tank before any loading commences.

Notable products under the IBC Code

Methanol

Methanol (Category Y, Type 2) is the most widely traded single chemical commodity in the bulk liquid sector. Its dual role as a petrochemical feedstock and as a fuel alternative places it at the intersection of the IBC Code’s safety provisions and the emerging regulatory framework for alternative marine fuels. Methanol’s toxicity (fatal oral dose in humans of approximately 70 to 100 mL) and its low flash point of 11°C require Type 2 carriage in tanks fitted with explosion-proof electrical equipment, controlled ventilation, and gas-detection systems calibrated to methanol. For its regulatory profile as a marine fuel, see methanol as a marine fuel. The methanol IBC profile gives its Chapter 17 requirements at a glance.

Monoethylene glycol (MEG)

Monoethylene glycol, CAS 107-21-1, is carried in larger volumes than almost any other single IBC-listed product. Its low acute toxicity, high flash point (111°C), and limited environmental hazard give it a Type 3 / Category Y assignment. Major trade routes connect ethylene crackers in the Middle East and North America with downstream polyester and antifreeze manufacturing in Asia. MEG is commonly carried on the same vessels as edible oils by virtue of its benign carriage requirements, but it is incompatible with strong oxidising acids and must not follow a cargo leaving acidic residues without a confirming wall-wash test. The MEG IBC profile provides applicable carriage conditions.

Benzene, toluene, and xylenes (BTX)

Benzene, toluene, and xylene isomers (commonly grouped as BTX aromatics) are high-volume petrochemical feedstocks produced at refinery reformers and moved to downstream chemical plants. Benzene (Category X, Type 2) is the most hazardous of the group by virtue of its human carcinogenicity - classified as Group 1 by IARC - and its significant vapour pressure (12.7 kPa at 25°C), requiring closed measurement systems, vapour-return connections, and periodic atmospheric monitoring. Toluene and the mixed xylenes carry Category Y / Type 2 assignments and are handled with similar equipment but without the mandatory prewash requirement.

Palm oil and edible oils

Palm oil (Category Y, Type 3) and other vegetable oils represent the largest cargo category by volume shipped in IBC-regulated vessels. The trade flows are dominated by exports from Indonesia and Malaysia to European, Indian, and Chinese import terminals. Palm oil solidifies below approximately 35°C and typically requires cargo heating to maintain pumpability. MEPC 75 in November 2020 reviewed updated ecotoxicological data on refined and crude palm oil fractions and confirmed Category Y status for the primary fractions. Operators carrying palm oil must satisfy the Chapter 17 requirements for cargo heating systems, non-pressurised deep-well or submerged electric motor pump systems, and tank coating compatibility, given that edible-grade palm oil is particularly sensitive to contamination from coating residues.

Phosphoric acid

Phosphoric acid (Category Y, Type 2 for concentrations above 70%, Type 3 for lower concentrations) is produced at phosphate-mining centres in Morocco, China, and Jordan and transported to global fertiliser-manufacturing facilities. Above 70% concentration it is highly corrosive to mild steel and requires 316L stainless steel or high-alloy tanks. The shipping community experienced a series of cargo heat incidents with high-concentration phosphoric acid in the 1990s that led to revised Chapter 15 guidance on temperature monitoring and heating system design for this product.

Caustic soda (sodium hydroxide solution)

Sodium hydroxide solution, typically at 50% weight-in-weight concentration, is a major industrial alkali transported from chlor-alkali plants to downstream users. It is a Category Y / Type 3 cargo at concentrations below 72%, non-flammable, and chemically stable under normal carriage conditions. Its high density (approximately 1,530 kg/m³ at 50%) and tendency to solidify below 12°C require heating during cold-weather voyages. The 2018 incident involving the vessel MSC Elsa 3, which reported a release of sodium hydroxide solution in the Mediterranean, illustrates the occupational hazard presented even by Type 3 alkalis: direct skin contact with 50% NaOH causes severe alkali burns within seconds, and the wash-down systems mandated by Chapter 8 of the IBC Code are essential for first-response decontamination.

Acetic acid

Acetic acid at concentrations above 80% (glacial acetic acid) is a Category Y / Type 2 cargo with a flash point of 40°C and significant corrosive properties towards mild steel. Below 80% concentration it is reclassified to Type 3. Major production centres include the carbonylation plants of major petrochemical complexes in Asia and the United States, with exports to downstream acetate ester, vinyl acetate, and PTA/PET production. Glacial acetic acid requires phenolic epoxy or stainless steel 316L tanks and specific venting arrangements to manage vapour accumulation.

Pumping and cargo transfer systems

IBC Code requirements for pumping and cargo piping are set out in Chapters 5 and 8. Each cargo tank must be equipped with an independent pumping system capable of discharging the cargo from the tank and stripping residues to the maximum extent practicable. The standard arrangement on modern chemical tankers is the deepwell pump: an electrically driven submerged centrifugal pump installed at the bottom of the cargo tank in a dedicated pump column. Deepwell pumps eliminate the need for suction lift from an external pump room and reduce the cross-contamination risk that arises when many cargoes share common pipeline sections. The cargo deepwell pump calculator gives the hydraulic performance parameters applicable to typical deepwell configurations.

Pump types and segregation

Deepwell pumps (submerged centrifugal type with electric motor above deck) have largely displaced the earlier hydraulic-drive submersible pumps on modern newbuilds, though hydraulic deepwells from manufacturers such as Framo remain common on existing fleet tonnage. Each dedicated pump serves a single tank, and the pump column and discharge line are physically separate from all other tanks. Cargo hose connections at the manifold are blanked off individually between operations, and line flushing procedures are performed before each new parcel connection to prevent carry-over contamination. The IBC Code’s Chapter 5 requirements for piping layout are particularly strict regarding separation between cargo lines and water service systems to prevent cross-contamination with ballast or cleaning water circuits.

Stripping efficiency - the ability to recover the maximum cargo volume from the tank before discharge ends - is critical for both commercial reasons (full delivery of the bill of lading quantity) and regulatory reasons (meeting the MARPOL Annex II 300-litre residue threshold). The chem-stripping-efficiency formula and chemtank-stripping-residue formula provide the quantitative basis for pre-discharge planning.

Vapour control and closed gauging

Chapter 14 of the IBC Code requires that tanks carrying products with vapour pressures above specified thresholds, or with toxic vapour hazards, be fitted with closed gauging systems. Open ullage measurement is prohibited for Category X products and for many toxic Category Y substances. Closed gauging systems typically comprise pneumatic ullage tapes, radar level gauges, or submerged float transmitters, all with vapour-sealed connections. For products with high vapour pressures, the vapour return connection at the manifold allows displaced vapour to return to shore storage during loading, preventing emission of toxic or flammable vapour to the atmosphere.

Inert gas and nitrogen padding requirements for reactive monomers and oxygen-sensitive products interact with the pumping system design: tanks under nitrogen blanket maintain slight positive pressure, and the deepwell pump penetration must be sealed to prevent air ingress at the pump-column stuffing box. The requirement to vent tanks to atmosphere during gravity drainage is specifically prohibited for products requiring closed-circuit handling.

Fire safety and vapour control

Flammable cargo categories

Many IBC-listed products are flammable liquids with flash points below 60°C - the threshold used in the Code to define flammability risk for tank arrangement and electrical equipment purposes. Chapter 12 of the IBC Code divides fire protection requirements into two product-driven classes: those for flammable products and those for non-flammable products. A tanker fitted with an inert gas system for oil tanker operations may not carry all IBC products under inert gas without additional design provisions, because certain monomers require oxygen to maintain inhibitor effectiveness.

Fixed fire-fighting systems on chemical tankers are typically high-expansion foam, dry powder, or water spray systems, applied selectively to the cargo manifold area and cargo tank deck. The choice of fire-fighting medium depends on the cargo: alcohol-resistant foam is required for water-miscible solvents such as methanol, ethanol, acetone, and MEG, since hydrocarbon-based foam is rapidly destroyed when it contacts these products. Chapter 12 specifies the firefighting agent, application rate, and fixed system coverage for each product category. Acetone (flash point −20°C) and similar ketones require explosion-proof electrical equipment throughout the cargo area and a continuous gas-detection system.

Inert gas and padding requirements

For reactive monomers and oxygen-sensitive cargoes, Chapter 15 permits two strategies to prevent polymerisation: nitrogen padding to maintain a slight positive pressure with inert atmosphere above the cargo, or controlled air padding to provide the oxygen level required by the inhibitor system without permitting accumulation of flammable or explosive concentrations. The choice is product-dependent and must be consistent with the product data sheet and the certificate of fitness entry.

Vinyl acetate monomer, methyl acrylate, ethyl acrylate, and methyl methacrylate require air padding - oxygen is an essential component of the inhibitor system for these peroxide-initiating polymerisations. Styrene monomer may be carried under either nitrogen or air padding depending on the inhibitor system used, with the requirement documented on the certificate of fitness. The carriage of any oxygen-requiring monomer aboard a vessel with a standard inert gas system therefore requires that the inert gas system be isolated from the relevant tanks and that a separate air supply line be available.

Closed gauging and atmospheric monitoring

Chapter 14 of the IBC Code specifies that products with vapour pressures exceeding 25 kPa at 37.8°C, or products with TLV-TWA values below specific thresholds, must be measured using closed or restricted gauging. Closed gauging systems maintain a full vapour seal at all measurement points. Portable instruments used to verify atmospheric concentrations above cargo tanks must be calibrated for the specific vapour - a benzene indicator calibrated in parts per million will not give valid readings for styrene vapour. The requirement for specific instrument calibration is particularly significant during cargo-to-cargo transitions when residues of the previous cargo may still be present at detectable concentrations.

Fixed gas-detection systems required by Chapter 13 for certain toxic cargoes continuously monitor for vapour breakthrough in the pump room, the cargo compressor room (where fitted), and at specified deck locations. Alarm setpoints are product-specific: benzene alarms typically activate at 0.5 ppm (approximately 10% of the TLV-TWA of 0.5 ppm) to provide a wide safety margin.

Incidents and enforcement

The Probo Koala incident (2006)

The Probo Koala affair remains the most widely documented environmental enforcement case directly involving a chemical tanker and toxic liquid waste disposal. The vessel, a converted oil tanker retrofitted to carry NLS cargoes, had taken on a large quantity of caustic washing residues containing hydrogen sulphide, mercaptans, and phenol compounds generated during the washing of gasoline storage tanks at the Amsterdam port terminal of Trafigura’s contractor. After multiple European ports declined to receive the waste at acceptable cost, the cargo was transferred at Abidjan, Côte d’Ivoire, to a local contractor who dumped approximately 500 tonnes of the liquid at 12 sites around the city in August 2006. The resulting hydrogen sulphide and mercaptan releases caused acute respiratory illness in tens of thousands of residents, with official Ivorian figures recording at least 17 deaths.

The Probo Koala incident did not constitute an IBC Code violation in the narrow technical sense - the wastes were not a Chapter 17 product - but it exposed the regulatory gap between the IBC Code’s product-specific carriage controls and the broader waste-handling provisions of the Basel Convention and MARPOL Annex V. The IMO and the European Commission responded with guidance tightening the definition of hazardous waste for purposes of the Reception Facilities Directive and clarifying the port state’s obligation to inspect waste reception procedures.

Port state control enforcement

Port state control examinations of chemical tankers, conducted by MoU member states including the Paris MoU, Tokyo MoU, and US Coast Guard under the authority of SOLAS Convention and MARPOL Convention, routinely check the COF and NLS Certificate validity, the Cargo Record Book completeness, the condition of inert gas or vapour control systems, and the operation of deepwell pumps and stripping systems. Deficiencies related to missing or expired COF entries for carried products, inadequate tank-cleaning records, and dysfunctional vapour control are consistent grounds for detention. Port state control procedures and detention criteria are described in port state control.

The ISM Code imposes complementary obligations on the chemical tanker operator’s safety management system to maintain documented procedures for cargo operations, cargo hazard assessment, and emergency response that are consistent with IBC Code requirements and with the chemical tanker operations chapters of the ISGOTT.

IMSBC Code

The IBC Code governs liquid bulk chemicals. The IMSBC Code governs solid bulk cargoes and provides the parallel regulatory framework for dry bulk commodities with hazardous properties. The two codes share the MARPOL pollution-category framework and a similar ship-type risk-based approach but differ substantially in the nature of the hazards addressed. The solid-liquid boundary is occasionally relevant for products that may be carried in either form (sulphur, for example, may move as molten sulphur under the IBC Code or as granular solid under the IMSBC Code).

MARPOL Annex II

MARPOL Annex II is the environmental enforcement arm of the IBC Code regime. While the IBC Code sets out construction and operational requirements aimed at preventing releases during normal operations, MARPOL Convention Annex II provides the discharge prohibitions, residue management obligations, and certification requirements that apply after cargo discharge. Annex II’s Regulation 18 requires that port states provide adequate reception facilities for NLS residues and prewash waters.

SOLAS Chapter VII

SOLAS Convention Chapter VII, Part B makes the IBC Code mandatory for new construction and sets out the applicable survey and certification obligations. SOLAS Regulation VII/16 requires that a ship carrying a substance listed in Chapter 17 of the IBC Code have a valid COF and carry a copy of the Code’s product list.

Classification society rules

Classification societies including Lloyd’s Register, Bureau Veritas, DNV, and ABS publish class notation rules for chemical tankers that typically go beyond the minimum IBC Code requirements in specifying tank inspection intervals, material certificates, and deepwell pump performance testing. The CSR (Common Structural Rules) applicable to tankers provide additional structural design standards. The classification society’s role in issuing the COF on behalf of the flag administration makes it the primary enforcement mechanism for IBC Code compliance at the construction stage.

Special purpose notation systems - for example DNV’s “Chemical Tanker” class notation, Lloyd’s Register’s “ChemSS” (Chemical Stainless Steel) notation, and Bureau Veritas’s “Chemical Tanker” and “ESP” (Enhanced Survey Programme) notations - specify mandatory inspection intervals for stainless steel tanks, coating condition assessments for epoxy and zinc silicate lined tanks, and functional testing of deepwell pumps and vapour control valves at each special survey. The IACS Unified Requirements for chemical tankers (UR P series) provide the shared technical baseline to which member societies align their individual rules, ensuring that a vessel classed with any IACS member society meets equivalent structural and equipment standards regardless of flag state.

STCW chemical tanker endorsements

The International Convention on Standards of Training, Certification and Watchkeeping for Seafarers (STCW Convention) requires that officers and ratings working aboard chemical tankers hold Basic Training for Chemical Tanker Cargo Operations and, at officer level, Advanced Training for Chemical Tanker Cargo Operations. These endorsements, introduced under the Manila Amendments (2010) and mandatory from 1 January 2012, establish minimum proficiency standards for cargo hazard recognition, use of personal protective equipment, emergency shutdown procedures, and tank entry protocols. The requirement applies to all vessels to which the IBC Code applies, and port state control officers verify STCW endorsements as part of chemical tanker inspections. Operators must ensure that no officer directs, or rating performs, cargo operations unless they hold the appropriate endorsement for the vessel type.

Pollution category X discharge prohibition: practical implications

The absolute prohibition on sea discharge of Category X residues has significant port infrastructure implications. A vessel discharging, for example, a benzene or vinyl chloride monomer cargo must complete an approved prewash and deliver the washings ashore before any tank opening or gas-freeing operation can begin. In practice this means that the discharging terminal must provide a functional reception facility - a slop tank, truck loading connection, or pipeline to a waste treatment facility - capable of accepting the prewash volumes at a rate compatible with the vessel’s washing equipment output. Where reception facilities are inadequate or expensive, operators have been known to schedule Category X discharges at ports with known reception capacity, sometimes at cost to voyage efficiency. The IMO’s Reception Facilities Secretariat maintains a database of port reception facilities, but coverage is incomplete for many Category X substances at smaller regional terminals.

Modern developments

Fleet size and commercial operators

The global chemical tanker fleet at the start of 2025 comprised approximately 4,600 vessels of varying size and capability. Parcel tankers - vessels with multiple independent stainless steel tanks carrying high-value chemicals - number around 600 deep-sea units above 10,000 dwt, dominated by operators including Stolt-Nielsen, Odfjell, Dow Chemical’s Oetkker-controlled Maersk Tankers segment, and Solvang. The mid-size segment (3,000 to 10,000 dwt) serving regional and short-sea trades contains several thousand more vessels, many with zinc silicate or epoxy-coated carbon steel tanks capable of carrying a narrower product range. Small coastal chemical tankers below 3,000 dwt, primarily operating under European and Asian coastal regulations, are numerous but are not always subject to the full IBC Code requirements that apply to ocean-going vessels.

The distinction between a chemical tanker operating under the IBC Code and a product tanker operating under MARPOL Annex I frequently depends on the cargoes actually carried: a vessel whose COF authorises carriage of IBC-listed products is a chemical tanker by certification, irrespective of its physical design. Many product tankers with high-quality coatings routinely carry vegetable oils (Type 3 / Category Y), ethanol, or MEG under an IBC COF while also carrying clean petroleum products under a separate MARPOL Annex I certificate - a practice that requires careful cargo sequence management and compatibility checking between consecutive cargoes.

Alternative fuels and dual-service vessels

The IBC Code’s detailed specifications for methanol, ethanol, and fatty acid methyl esters (FAME) as cargo commodities are increasingly cross-referenced by the emerging alternative fuel frameworks. Ships designed to use methanol as a marine fuel must satisfy both the IBC Code’s cargo carriage requirements (when methanol is the payload) and the IGF Code’s fuel containment requirements (when methanol is the bunker). The potential for a chemical tanker to carry methanol as both cargo and fuel on the same voyage creates a regulatory interface that IMO sub-committees have been working to clarify since MEPC 76 (2021).

Ammonia, listed in the IBC Code as a cargo (anhydrous ammonia under specific high-pressure conditions, and aqueous ammonia solutions at various concentrations), is attracting interest as a zero-carbon fuel. See ammonia as a marine fuel for the developing regulatory picture. The IBC Code’s Chapter 15 toxic vapour requirements for ammonia and the IGF Code’s draft ammonia fuel provisions are expected to converge as the IMO’s ammonia fuel safety regulatory framework matures.

MEPC 75 vegetable oil review

At MEPC 75 (November 2020) the committee reviewed the MARPOL Annex II categorisation of a number of vegetable oils, including palm oil, coconut oil, and palm kernel oil, against updated ecotoxicological data provided by industry and member states. The review considered the Environmental Hazard Evaluation (EHE) methodology introduced by the 2007 Annex II amendments. The outcome maintained Category Y for the major palm oil fractions, but the committee recognised that the methodology for evaluating chemically complex natural substances remained an area where further scientific work was warranted. A follow-up study commissioned by the IMO was expected to inform subsequent MEPC sessions.

Digital cargo planning and the ShipCalculators catalogue

The ShipCalculators.com calculator catalogue provides over 100 tools directly referencing IBC Code data, including individual product profiles for all Chapter 17 substances with their ship-type, pollution-category, coating, and heating requirements. These tools allow vessel operators, cargo brokers, and terminal operators to screen potential cargoes against COF limitations, estimate prewash volumes, calculate heating duty requirements, and confirm coating compatibility - all within a consistent framework traceable to the current IBC Code text and MEPC.2/Circ. guidance.

References

International Maritime Organization. International Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk (IBC Code). IMO, London, as amended (consolidating MEPC.20(22), MSC.4(48), and subsequent amendments through MEPC.271(69)).
IMO Resolution MEPC.20(22), 17 June 1983 - Adoption of the IBC Code under MARPOL Annex II.
IMO Resolution MSC.4(48), 17 June 1983 - Adoption of the IBC Code under SOLAS Chapter VII.
IMO Resolution MEPC.118(52), 15 October 2004 - Revised MARPOL Annex II, entering into force 1 January 2007.
IMO Resolution MEPC.166(56), 2 July 2008 - Amendments to the IBC Code for vegetable oils.
IMO Resolution MEPC.225(64), 2012 - Amendments to Chapter 17 and 18 of the IBC Code.
IMO Resolution MEPC.271(69), 2015 - Further amendments to the IBC Code cargo list.
MEPC.2/Circ. series - Annual IMO circulars on provisional categorisation of liquid substances. (Current year’s circular is the operative document for newly listed substances.)
MEPC 75th session, November 2020 - Review of vegetable oil categorisation under MARPOL Annex II.
International Maritime Organization. BCH Code (Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk). IMO, London, 1971 (as applicable to pre-1986 vessels).
Greenpeace International. The Probo Koala: A Crime Without Punishment. 2009 (background on the Abidjan waste dumping incident, August 2006).
ISGOTT. International Safety Guide for Oil Tankers and Terminals. Sixth edition. Witherby Seamanship International, 2020. (Sections on chemical tanker operations, vapour control, and tank entry.)
McGuire, G. and White, B. Liquefied Gas Handling Principles on Ships and in Terminals. Fourth edition. Witherby Seamanship International, 2016. (Background on volatile chemical cargo handling.)
UK P&I Club. Guide to Bulk Liquid Cargoes. (Practical guide to chemical tanker cargo claims and contamination issues.)