IBC Code: chemical tanker construction and carriage rules

The International Bulk Chemical Code (IBC Code) is the IMO instrument that sets how a ship carrying dangerous liquid chemicals in bulk must be built, equipped and operated. It was adopted by IMO resolution MSC.4(48) on 17 June 1983, and it applies to every chemical tanker constructed on or after 1 July 1986. Its chapter 17 is the operative list: for each product it names the ship type, the tank type, the venting and environmental control, the electrical standard, the gauging, the vapour detection and the fire protection that product demands.

Two features of the Code catch practitioners out. It reaches a ship by two separate legal routes, safety through SOLAS chapter VII and pollution through MARPOL Annex II , so an amendment can arrive under one and not the other. And a great deal of what governs a chemical tanker in practice, from the cargo compatibility chart to the wall wash acceptance limits to the coating resistance list, is not in the Code at all.

The two instruments that make the Code mandatory

The IBC Code became mandatory under SOLAS through chapter VII, by the 1983 SOLAS amendments adopted in IMO resolution MSC.6(48) on 17 June 1983, the same day as the Code itself. MSC.4(48) records the connection in terms, noting MSC.6(48) as the resolution by which the Committee adopted amendments to SOLAS chapter VII to make the provisions of the Code mandatory under that Convention. Both took effect on 1 July 1986, which is why that date divides the whole chemical tanker fleet.

The pollution half arrived separately and later. IMO resolution MEPC.19(22) adopted the IBC Code under MARPOL Annex II on 5 December 1985, and MEPC.16(22) of the same date made both it and the BCH Code mandatory under the Annex. MARPOL Annex II regulation 11.1.1 applies the Code to chemical tankers constructed on or after 1 July 1986.

Getting the resolution numbers right matters, because two of them are adjacent and are routinely swapped. MEPC.20(22), also of 5 December 1985, adopted the BCH Code extended to cover marine pollution aspects. It is not the IBC Code resolution. Amendments to the Code are made through SOLAS article VIII(b) and regulation VII/8.1 on the safety side, and through MARPOL article 16 and Annex II regulation 1.4 on the pollution side, which is why a revision usually arrives as a pair of resolutions on the same day.

The BCH Code, and what 1 July 1986 divides

A chemical tanker constructed before 1 July 1986 falls under the Code for the Construction and Equipment of Ships Carrying Dangerous Chemicals in Bulk, the BCH Code , adopted by IMO Assembly resolution A.212(VII) on 12 October 1971. IMO resolution MEPC.20(22) of 5 December 1985 adopted the version extended to cover marine pollution aspects, and MEPC.16(22) made it mandatory under MARPOL Annex II.

Its status is split, which is easy to miss. The BCH Code remains a recommendation under SOLAS 1974 and a mandatory instrument under MARPOL Annex II. Regulations 11.1.2 and 11.1.3 route the pre-1986 ships to it: 11.1.2 covers ships contracted on or after 2 November 1973 but built before 1 July 1986 on international voyages, and 11.1.3 covers ships contracted before 2 November 1973.

The practical residue of that split is small and shrinking, because a chemical tanker built before mid-1986 is now around forty years old. It still matters when reading a certificate: a BCH Code ship holds a Certificate of Fitness issued under that Code, not under the IBC Code, and the product lists are not interchangeable.

Twenty-one chapters, and what each one holds

The Code has twenty-one chapters, not twenty, which is a common miscount because chapter 21 was a late addition and older summaries stop at 20.

Chapter 1 general; 2 ship survival capability and location of cargo tanks; 3 ship arrangements; 4 cargo containment; 5 cargo transfer; 6 materials of construction; 7 cargo temperature control; 8 cargo tank venting and gas-freeing arrangements; 9 environmental control; 10 electrical installations; 11 fire protection and fire extinction; 12 mechanical ventilation in the cargo area; 13 instrumentation; 14 personnel protection; 15 special requirements; 16 operational requirements; 17 summary of minimum requirements; 18 list of products to which the Code does not apply; 19 index of products carried in bulk; 20 transport of liquid chemical wastes; and 21 criteria for assigning carriage requirements for products subject to the Code.

Four of those numbers are worth committing to memory because secondary sources get them wrong so often. Materials of construction is chapter 6, not chapter 15. Fire protection and fire extinction is chapter 11, not 12. Instrumentation is chapter 13, with gauging at 13.1 and vapour detection at 13.2. Personnel protection, including the wash-down and safety shower provisions, is chapter 14. Chapter 9, environmental control, and the enclosed space entry discipline that follows from it sit alongside.

Chapter 15, special requirements, is a list of named products and conditions rather than a systematic chapter, running from ammonium nitrate solution and carbon disulphide through hydrogen peroxide, phosphorus, propylene oxide and molten sulphur to acids, toxic products, cargoes protected by additives, and high vapour pressure cargoes. Column o of chapter 17 is what pulls the right chapter 15 paragraph into a given product’s requirements.

Ship types 1, 2 and 3

Chapter 2.1.2 defines the three types by hazard severity, and the wording is worth quoting because the distinctions are graded rather than categorical.

A type 1 ship is a chemical tanker intended to transport chapter 17 products with very severe environmental and safety hazards which require maximum preventive measures to preclude an escape of such cargo. A type 2 ship carries products with appreciably severe hazards which require significant preventive measures. A type 3 ship carries products with sufficiently severe hazards which require a moderate degree of containment to increase survival capability in a damaged condition.

The type for each product is column e of chapter 17, and since 1 January 2021 the criteria that set it are explicit and quantified in chapter 21 paragraph 21.4.5.2: inhalation LC50 or acute toxicity estimate with the saturated vapour concentration to LC50 ratio, dermal LD50 or acute toxicity estimate, the water reactivity index, the auto-ignition temperature, the explosive range read with the flashpoint, and the pollution rules worked from the GESAMP profile. Chapter 2.1.4 handles the multi-product ship: it takes the most stringent damage standard of any product it is certified for, but the cargo tank location requirement follows the ship type of the product actually carried in that tank.

Damage assumptions and where the cargo tanks must sit

Chapter 2.5 fixes the damage the ship is assumed to take. Side damage extends longitudinally by L to the power two-thirds divided by three, or 14.5 m, whichever is less; transversely by B/5 or 11.5 m, whichever is less, measured inboard at right angles to the centreline at the summer load line; and vertically upwards without limit. Bottom damage within 0.3L of the forward perpendicular takes the same longitudinal extent, a transverse extent of B/6 or 10 m and a vertical extent of B/15 or 6 m, each whichever is less. Elsewhere along the ship the longitudinal and transverse bottom figures both fall to 5 m.

Chapter 2.6.1 turns those assumptions into steel. On a type 1 ship the cargo tanks sit inboard from the side shell by not less than the transverse extent of side damage, B/5 or 11.5 m whichever is less, and above the moulded line of the bottom shell at centreline by not less than the vertical extent of bottom damage, B/15 or 6 m whichever is less, and nowhere less than 760 mm from the shell plating. On a type 2 ship only the bottom distance applies, with the same 760 mm minimum; the Code sets no side-shell inboard distance for a type 2 ship. A type 3 ship has no cargo tank location requirement at all.

Chapter 2.6.2 allows a suction well to protrude into the vertical extent of bottom damage on any ship except a type 1, provided the well is as small as practicable and the protrusion below the inner bottom does not exceed 25 percent of the double bottom depth or 350 mm, whichever is less.

Chapter 2.8.1 then scales the standard of damage by type and by length. A type 1 ship must survive damage anywhere in its length. A type 2 ship over 150 m likewise; at 150 m or less, anywhere except damage involving either bulkhead bounding an aft machinery space. A type 3 ship over 225 m anywhere; from 125 m to 225 m anywhere except those machinery space bulkheads; below 125 m anywhere except the machinery space itself, with survival of machinery space flooding left to the Administration. There is no two-adjacent-tank flooding standard anywhere in chapter 2.

Reading a chapter 17 row

Chapter 17 is the summary of minimum requirements and the part of the Code a chief officer actually opens. Chapter 21.4 defines each column, and the row reads left to right from the product name to the requirements it triggers.

A worked row makes it concrete. Acrylonitrile reads: Y, S/P, 2, 2G, Cont, No, T1, IIB, No, C, FT, AC, Yes, 15.12, 15.13, 15.17, 15.19. That is a category Y pollutant, in the Code for both safety and pollution, carried on a ship type 2 in an integral gravity tank with controlled venting and no environmental control, needing T1 apparatus in group IIB, a flashpoint at or below 60 degrees C, closed gauging, both flammable and toxic vapour detection, alcohol-resistant foam and water spray, emergency equipment, and four chapter 15 special requirements on top.

The temperature class in column i is the auto-ignition band the cargo-area electrical equipment must be certified for: T1 at 450 degrees C or above, T2 from 300 to below 450, T3 from 200 to below 300, T4 from 135 to below 200, T5 from 100 to below 135, and T6 from 85 to below 100.

Chapter 18 is the list of products to which the Code does not apply: substances assessed and found to present no safety or pollution hazard sufficient to bring them into chapter 17. It is short, and the 2019 revision made it much shorter: after those amendments it carries 32 entries, from acetone through water, split between category Z and OS, because a large number of former chapter 18 products were moved into chapter 17 and now need a Certificate of Fitness.

Chapter 19 is the index of products carried in bulk, a synonym-to-product-name index carried for information. Paragraph 19.3 is the trap: none of its lower-case index names may be used as the product name on the shipping document. The 2019 revision removed its UN number column. A liquid appearing in neither chapter 17 nor chapter 18 cannot be carried until it has been assessed.

MARPOL Annex II: the four categories and what may be discharged

MARPOL Annex II regulation 6.1 sorts every noxious liquid substance into four categories by the harm a discharge would do. Category X presents a major hazard and its discharge is prohibited. Category Y presents a hazard or harm to amenities and carries limitations on both the quality and the quantity discharged. Category Z presents a minor hazard with less stringent restrictions. OS covers other substances, shown as OS in the pollution category column of IBC chapter 18, evaluated and found to fall outside X, Y and Z; a discharge of bilge water, ballast or residues containing only OS is not subject to any requirement of the Annex.

Assignment is technical, not commercial. Regulation 6.2 routes it to the criteria in appendix 1 to the Annex, worked from the product’s GESAMP hazard profile covering bioaccumulation, biodegradation, acute and chronic aquatic toxicity, long-term health effects and effects on marine wildlife and the seabed. The categorization of noxious liquid substances is the gateway to everything else in the Annex.

One discharge standard covers X, Y and Z alike. Regulation 13.2.1 requires the ship to be en route at not less than 7 knots if self-propelled or 4 knots if not; the discharge to be made below the waterline through the underwater outlet at not more than its design rate; and the position to be not less than 12 nautical miles from the nearest land in water not less than 25 m deep. The pre-2007 rate limits of one cubic metre per nautical mile and one three-thousandth of tank capacity belonged to the old Category B and C regime and are gone. Regulation 13.8 prohibits any discharge of noxious liquid substances south of latitude 60 degrees South, with no allowance at all.

Category Z is not a lighter discharge standard, which is a common misreading. A category Z cargo takes the same regulation 13.2 discharge conditions and the same 75 litre stripping limit on a post-2007 ship. What it gets is four narrower reliefs: no prewash trigger of its own, no mandatory underwater discharge outlet on a ship built before 1 January 2007, no mandatory below-waterline discharge on such a ship, and a possible waiver of the 12 nautical mile distance for a domestic voyage.

Regulation 12 sets what may be left in the tank. A ship constructed on or after 1 January 2007 must strip to not more than 75 litres per tank and its associated piping, for categories X, Y and Z alike. Older tiers are looser: 100 litres for X and Y with 300 for Z on ships built from 1 July 1986 to before 1 January 2007, and 300 and 900 litres respectively before that. Performance is proved by a water test under appendix 5 approved by the Administration. See regulation 12 on pumping, piping and unloading arrangements . The frequently quoted 300 litre figure is the pre-1986 standard, and repeating it as current understates the requirement by a factor of four.

When a prewash is required

Four cases, each with its own regulation, and they are commonly conflated.

A category X tank is prewashed before the ship leaves the port of unloading, under regulation 13.6.1.1. The residues go to a reception facility until the effluent concentration is at or below 0.1 percent by weight on analysis of a surveyor-taken sample, and washings then continue to the facility until the tank is empty. The prewash procedures themselves are in appendix 6 to the Annex, not in regulation 13. The Cargo Record Book entries are endorsed by the surveyor appointed under regulation 16.1.

A category Y or Z tank is prewashed under regulation 13.7.1.2 only where unloading was not carried out in accordance with the Procedures and Arrangements Manual . Compliance with the Manual is what avoids the prewash, which is why the Manual is the document a port state control officer reaches for first.

A high-viscosity or solidifying category Y substance takes the appendix 6 prewash under regulation 13.7.1.3, with discharge to a reception facility until the tank is empty. Regulation 1 defines a high-viscosity substance as category X or Y with a viscosity of 50 mPa.s or more at the unloading temperature, and a solidifying substance by its melting point against the unloading temperature: melting point below 15 degrees C and unloaded at less than 5 degrees C above it, or melting point at 15 degrees C or above and unloaded at less than 10 degrees C above it.

Regulation 13.4 allows the receiving Government to exempt a tank from prewash on the master’s request, on three stated grounds. Regulation 13.3 covers ventilation of cargo residues under appendix 7.

Persistent floating products, and where that rule bites

IMO resolution MEPC.315(74), adopted 17 May 2019 and in force 1 January 2021, added a fourth prewash case and a new definition. Regulation 1.23 defines a persistent floater by four properties together: density not more than that of sea water at 1,025 kg/m3 at 20 degrees C, vapour pressure not more than 0.3 kPa, solubility not more than 0.1 percent for a liquid or 10 percent for a solid, and kinematic viscosity greater than 10 cSt at 20 degrees C. The practical description is a slick-forming cargo that neither evaporates nor dissolves.

Regulation 13.7.1.4 then requires an appendix VI prewash for a category Y persistent floater with a viscosity of 50 mPa.s or more at 20 degrees C and, or, a melting point of 0 degrees C or more, identified by the entry 16.2.7 in column o of IBC chapter 17. The residue and water mixture goes to a reception facility at the port of unloading until the tank is empty.

This is a regional rule, not a global one. Regulation 13.9 lists the areas: North West European waters, the Baltic Sea area, Western European waters and Norwegian waters. Note also that the high-viscosity test at regulation 1 is taken at the unloading temperature while the persistent floater test is taken at 20 degrees C, so a cargo can meet one and not the other. The revised standard format of the Procedures and Arrangements Manual carries the persistent-floater procedures, so a conforming approved Manual had to be aboard from 1 January 2021.

Certification: the Certificate of Fitness and the NLS Certificate

IBC Code section 1.5 covers surveys and certification. After an initial or renewal survey the Administration issues the International Certificate of Fitness for the Carriage of Dangerous Chemicals in Bulk , in the form set out in the appendix to the Code, for a period not exceeding five years. The certificate names the products the ship may carry, so adding a product is a certificate amendment rather than an operational decision, taken by the flag State on the advice of its recognized organization .

The survey cycle at section 1.5.2.1 runs: an initial survey before the ship is put in service; a renewal survey at intervals not exceeding five years; an intermediate survey within three months before or after the second or third anniversary date, replacing one annual survey; an annual survey within three months of each anniversary date; and an additional survey after a repair or renewal. Section 1.5.6.4 permits an endorsement extending validity by not more than five months where the renewal survey is complete but the certificate cannot be placed on board before expiry, and 1.5.6.6 gives a short-voyage grace period of up to one month. Under 1.5.6.9 the certificate ceases to be valid where surveys are not completed in time, where it is not endorsed, or on transfer of flag.

The NLS Certificate, the International Pollution Prevention Certificate for the Carriage of Noxious Liquid Substances in Bulk under MARPOL Annex II regulation 9 , is the narrower document, covering the pollution requirements alone.

A chemical tanker holding a Certificate of Fitness needs no separate NLS Certificate. Annex II regulation 7 provides that the Certificate of Fitness has the same force and receives the same recognition as the NLS Certificate. The ship that holds an NLS Certificate alone is the noxious liquid substance tanker that is not a chemical tanker: an Annex I oil tanker certified for a part cargo of noxious liquid substances, or a dry cargo ship carrying vegetable oil in deep tanks. Holding both is the exception, not the rule. The model form of the Certificate of Fitness was itself replaced by IMO resolution MEPC.302(72) with effect from 1 January 2020. See regulation 7 on chemical tanker survey and certification , regulation 8 on surveys and regulation 10 on certificate duration and validity .

How a new chemical reaches chapter 17

Through MARPOL Annex II regulation 6.3, the provisional assessment route. For a liquid not yet categorized, the Governments involved establish and agree a provisional assessment, and until they fully agree, the substance shall not be carried. The producing or shipping country notifies IMO not later than 30 days after agreement, IMO circulates the assessment annually to all Parties and maintains a register, and the product is eventually formally included in the Code by amendment.

That annual circulation is the MEPC.2 circular , issued each December, and it is where a cargo appears while it is still provisional. The current edition is MEPC.2/Circ.31 of 1 December 2025, which replaces all previously issued circulars under that title and carries twelve annexes, from list 1 of pure and technically pure products through lists of trade-named mixtures, vegetable oil synonyms, tripartite contact addresses, cargo tank cleaning additives and biofuels.

A provisional entry does not last indefinitely. Under the guidelines at MEPC.1/Circ.512/Rev.1, a tripartite agreement runs for three years and then expires permanently, and no new agreement may be made for the same product; each list 1 entry that rests on one carries an explicit expiry date. The route to a permanent entry runs through the GESAMP hazard evaluation working group, which assigns the hazard profile, and then the ESPH technical group of the Sub-Committee on Pollution Prevention and Response, which assigns the carriage requirements; a fully assessed product appears with no expiry and is folded into the Code at the next amendment.

The circular is not a compatibility chart, which is a persistent misdescription: it carries provisional categorizations and carriage requirements, nothing more. See provisional assessment of noxious liquid substances .

Cargo compatibility, and whose chart it is

The IMO publishes no cargo compatibility chart. The chart the industry uses worldwide is 46 CFR part 150, Compatibility of Cargoes , a United States Coast Guard regulation. It assigns each cargo to a reactive group numbered 1 to 22, or to a cargo group numbered 30 to 43, and an X at the intersection of two groups on Figure 1 means the pair is incompatible. Cargo groups appear only on the left axis and do not react hazardously with one another.

The underlying criterion, in appendix II to the part, is that a binary mixture is treated as hazardous where the temperature rise exceeds 25 degrees C or a gas is evolved under the test conditions. Appendix I lists tested combinations found not to be dangerously reactive, which are the exceptions permitted in adjacent tanks, and appendix III gives the test method.

The distinction to keep straight is legal. Inside United States waters the chart is law. Outside them it is convention, and a chemical tanker operator worldwide is applying a United States regulatory artefact as commercial practice because it is the only published chart of its kind.

Materials and coatings: what the Code requires, and what it leaves to the market

Chapter 6 requires materials of construction and linings resistant to the cargo. It does not name a coating, a grade or a thickness. Which lining a tank carries is a commercial and class approval matter, governed in practice by the coating manufacturer’s cargo resistance list, which is contractual rather than regulatory.

The modern deep-sea parcel tanker is built in bare duplex stainless steel, typically 2205 to UNS S32205, or the older and wider S31803, EN 1.4462, in integral corrugated tanks rather than independent ones. Three properties earn it the place: a minimum yield strength around 450 MPa against roughly 200 MPa for 316L, so plate can be thinner; a nominal 3 to 3.5 percent molybdenum that widens the carriable cargo list; and a coefficient of thermal expansion closer to carbon steel than that of 304 or 316, which matters because a stainless tank sits inside a carbon steel hull. The metallurgy is set out in duplex and super duplex stainless steel .

On coated carbon steel three families dominate, and each has a hard boundary.

• Inorganic zinc silicate suits aromatic hydrocarbons, alcohols and ketones. It is attacked by acids and alkalis including sea water, which makes long ballast legs a problem, and it carries a metallic zinc pick-up risk that rules it out for foodstuffs and aviation fuels. It is not suited to vegetable oils or animal fats, and the frequent claim that it is the coating of choice for tanks alternating between vegetable oil and petroleum fractions inverts the manufacturer’s own guidance.
• Novolac phenolic epoxy covers a wider acid and alkali range, is normally applied in two or three coats, and on some products requires a heat post-cure before an aggressive cargo. Its resistance to amines is very limited.
• Siloxirane coatings are marketed for acids, alkalis and solvents together and leave the yard fully cured. The performance claims for them come from the manufacturer and should be read as such.

The practitioner term for what a coated tank does after an aggressive cargo is coating memory: the lining absorbs cargo and releases it slowly, which is why a wall wash result on a coated tank needs more careful reading than one on bare stainless.

Wall wash testing is a commercial gate, not a regulation

No provision of the IBC Code or of MARPOL Annex II requires a wall wash test . It exists because the cargo buyer writes a purity specification into the voyage instructions and the loading terminal’s independent surveyor takes tank-wall samples for shore laboratory analysis. Failing it does not make the ship non-compliant. It makes the ship unable to load that parcel, which is commercially worse.

The limits come from the product specification. For methanol, the commonest case, that is the IMPCA Methanol Reference Specifications, version 10 of 25 October 2024, whose parameters include a permanganate time of at least 60 minutes at 15 degrees C by ASTM D1363, a platinum-cobalt colour of 5 maximum by ASTM D1209, chloride at 0.5 mg/kg maximum by IMPCA 002-98, and a hydrocarbon miscibility pass by ASTM D1722. Those are limits set by a producers and consumers association, and the shipboard result is indicative: the loading decision rests on the surveyor’s samples analysed ashore. See marine tank cleaning .

Inhibited cargoes, and the conflict with inerting

IBC Code 15.13, cargoes protected by additives , governs a monomer carried with a chemical inhibitor that suppresses polymerisation. Paragraph 15.13.3 requires the ship to be provided with a certificate of protection from the manufacturer, a requirement introduced by IMO resolution MEPC.55(33) of 30 October 1992. The certificate states the inhibitor, its concentration, the date it was added and the period for which it remains effective.

Some inhibitors need oxygen to work, which sets up a direct conflict with inerting. Styrene monomer is inhibited with 4-tert-butylcatechol, which is oxygen-dependent, so nitrogen blanketing would disable the barrier that stops polymerisation. Producer cargo handling sheets set a floor rather than leaving it to judgement: Shell’s styrene monomer sheet, revision 17 of 5 May 2023, requires nitrogen as the only acceptable inerting medium and states that oxygen in the vapour space shall at no time fall below 4 percent by volume. The band is narrow because the limiting oxygen concentration for styrene combustion is around 9 percent by volume. Acrylic acid is the same case with MEHQ, and the producer instruction is not to blanket with nitrogen at all.

Acrylic acid carries a second hazard the inhibitor rule does not cover. It freezes at 13 degrees C, and MEHQ concentrates in the liquid phase during partial freezing, so thawed material can be under-inhibited. The cargo is held between about 18 and 25 degrees C for that reason, and improper thawing is itself the hazard.

The Code resolves the conflict by deferring the inerting. Paragraph 15.13.5 provides that where a product contains an oxygen-dependent inhibitor and the ship is required to be inerted, inert gas shall not be applied before loading or during the voyage, but shall be applied before commencement of unloading. SOLAS regulation II-2/16.3.3 mirrors that for a chemical tanker and adds that only nitrogen may be used. The unified interpretation is MSC-MEPC.5/Circ.10 of 23 June 2015.

One trap sits just outside the Code. Butadiene is inhibited with the same 4-tert-butylcatechol, but there the inhibitor is not oxygen-dependent: the control barrier is the exclusion of oxygen, because oxygen forms peroxides in butadiene. Butadiene is also a liquefied gas carried under the IGC Code, not the IBC Code, so neither the 15.13.5 rule nor the styrene reasoning transfers to it.

The inert gas requirement most chemical tankers now meet

SOLAS regulation II-2/4.5.5, as amended by IMO resolution MSC.365(93) and in force from 1 January 2016, requires a fixed inert gas system on tankers of 8,000 tonnes deadweight and over with a keel laid on or after that date, carrying cargoes with a flashpoint below 60 degrees C. The previous threshold was 20,000 dwt. The same package cut the permitted oxygen content of inert gas supplied to cargo tanks from 8 percent to 5 percent.

The older waiver for chemical tankers with small cargo tanks and limited-throughput washing machines survives only for ships constructed before 1 January 2016. A chemical tanker keel-laid on or after that date and carrying flammable chapter 17 or 18 cargoes needs a fixed system regardless of tank size, which is precisely why the 15.13.5 sequencing rule matters more now than it did. See marine inert gas systems .

Cargo pumps, segregation and the pump room

One cargo pump per tank is the defining architecture of the parcel tanker, and it is what produces segregation: a dedicated pump means no shared suction line between parcels, so many different cargoes can be carried, loaded and discharged independently without cross-contamination. Two families compete, both one-per-tank. Hydraulically driven submerged centrifugal pumps sit at the tank bottom fed from a central hydraulic power pack, with stepless capacity control and no overload or overspeed limit. Electric deepwell pumps drive the impeller through a long shaft from a motor on deck.

Putting a submerged pump in each cargo tank and submerged ballast pumps in the double-side tanks removes the need for a pump room altogether, which is the standard modern arrangement and adds cargo space. Segregation counts follow from the tank count: a general product and chemical tanker without a pump room typically carries six to eight cargo segregations, while the current deep-sea stainless newbuildings of about 38,000 dwt under construction for delivery from 2026 to 2028 carry 30 stainless steel cargo tank segregations. See marine cargo pumps and piping and tanker size classes .

Products, ship types and the vegetable oil exemption

A product carries two independent labels and they answer different questions. The ship type in column e is a survivability and containment standard set by hazard severity, and it governs how the ship is built. The pollution category in column c is set by the GESAMP hazard profile, and it governs what may be discharged. A type 3 ship can carry a category Y product; a type 2 ship can carry a category Z one.

Methanol is ship type 3, pollution category Y. It was proposed for stricter treatment during the chapter 21 revision and returned to type 3 once new product data was submitted, so older sources listing it as type 2 are out of date.

Vegetable oils, including palm oil, moved from type 3 to type 2 with effect from 1 January 2007. Because that created a tonnage shortfall, MARPOL Annex II regulation 4.1.3 lets a flag Administration exempt a ship certified for the vegetable oils identified by the letter k in chapter 17 from the regulation 11 carriage requirements. The technical shape of the exemption is a type 3 ship with type 2 cargo tank location: every type 3 requirement is met except tank location, and the tanks are placed to type 2 standard through the whole cargo tank length. It is endorsed on the Certificate of Fitness.

A dry cargo ship can carry vegetable oil in bulk by a different route entirely. IMO resolution MEPC.148(54), adopted 24 March 2006 and in force 1 January 2007, carries the revised guidelines for transporting vegetable oils in deep tanks or specially designed independent tanks on general dry cargo ships, superseding MEPC.120(52). Such a ship stays subject to the Annex II discharge requirements, carries a Procedures and Arrangements Manual and is certified under Annex II regulation 10.1, and holds no Certificate of Fitness.

What the 2019 amendments changed

IMO resolutions MSC.460(101), adopted by the Maritime Safety Committee on 13 June 2019, and MEPC.318(74), adopted by the Marine Environment Protection Committee on 17 May 2019, both in force 1 January 2021, are the most recent major revision. They revised chapters 17, 18, 19 and 21 together.

Three effects matter operationally. Many products had their ship type upgraded, from 3 to 2 and from 2 to 1. Several cargoes moved out of chapter 18 into chapter 17 with pollution category Z, so that they can no longer be carried without a Certificate of Fitness. And the toxic designation T was added in column k to a large number of cargoes, which requires vapour detection instruments on board for those products. The companion resolution MEPC.315(74), of the same date and in force the same day, created the persistent floater prewash regime described above.

The driver behind all of it was chapter 21. That chapter is the criteria set that assigns every column of chapter 17, so once it was rewritten every product entry had to be reassessed against it. The revision also deleted two columns outright: column b, the UN number, and column m, materials of construction.

The practical consequence for an operator was a certificate review rather than a shipyard visit: a ship whose product list included an upgraded cargo needed its Certificate of Fitness reissued and on board by 1 January 2021, and one carrying a newly T-designated cargo needed the detection equipment aboard. A transitional rule covered the crossover: a cargo loaded before an amendment enters into force and unloaded after it keeps the provisions that were in force at loading.

The most recent amendments to the Code are the 2022 pair, IMO resolutions MSC.526(106) and MEPC.345(78), in force 1 July 2024. They are narrow, amending paragraph 2.9.2.1 on doors in watertight bulkheads to align the Code’s survivability conditions with the equivalent SOLAS and IGC provisions. No IBC Code amendment is currently adopted and awaiting entry into force.

Which instrument governs a bulk liquid cargo

Three regimes divide the bulk liquid trades, and the boundary is the nature of the cargo rather than the ship.

The Code draws its own outer edge at paragraph 1.1.3: the liquids it covers are those having a vapour pressure not exceeding 0.28 MPa absolute at 37.8 degrees C. Above that threshold the cargo is a liquefied gas and falls to the IGC Code . Paragraph 1.1.1 draws the other edge, applying the Code to ships of any size, including those under 500 gross tonnage, carrying dangerous chemicals or noxious liquid substances other than petroleum or similar flammable products, so oil as MARPOL Annex I defines it goes to Annex I and the oil tanker regime. Solid bulk cargoes go to the IMSBC Code , and packaged dangerous goods to the IMDG Code under SOLAS chapter VII .

A ship can move between regimes on successive voyages, which is where the changeover procedures matter: an Annex I to Annex II cargo changeover has its own cleaning and documentation sequence, and the industry guidance for it sits in the ICS Tanker Safety Guide (Chemicals) rather than in the Code.

Manning, training and the industry inspection layer

STCW regulation V/1-1 sets the training requirement. The competence standard for basic training in oil and chemical tanker cargo operations is table A-V/1-1-1, a single combined basic table covering both trades. Advanced training for chemical tanker cargo operations is table A-V/1-1-3, distinct from A-V/1-1-2 for advanced oil. The advanced chemical standard is what a master, chief engineer, chief mate, second engineer or any officer with immediate responsibility for cargo must hold. See STCW chapter V special training .

On top of the statutory layer sits a private one with no legal force and considerable commercial force. The OCIMF Ship Inspection Report Programme moved to SIRE 2.0, and the earlier VIQ7 questionnaire was retired, on 2 September 2024. The Chemical Distribution Institute’s Marine Ship Inspection Report reached its 10th edition, version 10.5, live from 5 February 2024, with its scope widened beyond chemical and LPG to LNG, product and dry bulk, and with every question categorized as statutory, recommended or desirable. That three-way categorization is the clearest published statement anywhere of the difference between an IMO requirement, an industry code of practice and a customer preference.

A chemical tanker can be fully compliant with the IBC Code and commercially unemployable on a poor inspection report. See SIRE tanker inspections , vessel vetting and charterer vetting policies .

Two casualties that define the subject

Bow Mariner , 28 February 2004. The Singapore-flagged chemical tanker was lost about 45 nautical miles off the Virginia coast with 21 of her 27 crew. She had discharged MTBE from 22 tanks at New York on 25 February, and the master ordered those tank lids opened for cleaning although the tanks had been neither washed nor mechanically ventilated. Their atmospheres were above the upper explosive limit, so admitting air brought them into the flammable range and released heavier-than-air vapour on deck. Two explosions followed less than two minutes apart and the ship sank in about an hour and a half. The United States Coast Guard, investigating on behalf of the flag State, found that inerting was not required by the regulations then applicable to that ship but was required by the operator’s own safety management system and was not used, and that the general alarm was never sounded. The case is the standing demonstration that a tank atmosphere above the upper explosive limit is not a safe atmosphere.

Stolt Groenland , 28 September 2019. A cargo tank on the Cayman Islands-flagged chemical tanker burst at Ulsan, Republic of Korea, from runaway polymerisation of a styrene monomer cargo, and the released vapour ignited; the emergency response ran over six hours and involved more than 700 personnel. The UK Marine Accident Investigation Branch, investigating on behalf of the Red Ensign Group, published report 9/2021 on 20 July 2021. Its findings were that the styrene monomer was affected by heat from other heated cargo tanks, that the heat transfer to adjacent cargoes was not fully appreciated, and that the styrene monomer temperature was not monitored. Recommendations went to the Cayman Islands Shipping Registry, the Chemical Distribution Institute and Plastics Europe to make the guidance in inhibitor certificates and styrene handling guides consistent and achievable given the limitations of shipboard equipment.

The two cases sit either side of the Code. Bow Mariner is a gas-freeing and safety-management failure; Stolt Groenland is an inhibited-cargo and temperature-monitoring failure that reaches directly into IBC 15.13 and the certificate of protection.

Limitations

This article states the IBC Code as amended by IMO resolutions MSC.460(101) and MEPC.318(74), in force since 1 January 2021, and MARPOL Annex II as revised by MEPC.118(52) and amended by MEPC.315(74). It is a reference summary and not a substitute for the Code, the Annex, the ship’s Certificate of Fitness product list or the Procedures and Arrangements Manual, each of which governs a specific ship and a specific cargo.

Four limits are worth naming. No total chemical tanker fleet count is given here, because published counts range from roughly 4,600 to over 8,700 vessels depending entirely on whether coastal and inland tonnage is included, and the figures that circulate come from paywalled broker research rather than from a citable primary source. The chapter 17 ship type and pollution category of an individual product is not restated here except where verified, because those entries change by amendment and the Code itself is the only safe reference. Coating dry film thicknesses and tank surface roughness figures are omitted for the same reason: they are manufacturer and specification values, not Code values. And the compatibility, wall wash and vetting layers described above are commercial regimes, not regulation, and a ship can satisfy every one of them and still fail an Annex II inspection, or the reverse.

Where this article distinguishes an IMO requirement from class practice from commercial practice, that distinction is load-bearing. A great deal of what a chemical tanker actually does at a berth is driven by a cargo resistance list, a product specification or a charterer’s guidelines, none of which is enforceable by a port state control officer and all of which can stop the ship loading.

Related Articles

• Chemical tanker
• MARPOL Annex II
• MARPOL Annex II regulation 6: categorization of noxious liquid substances
• MARPOL Annex II regulation 11: cargo tank arrangement
• MARPOL Annex II regulation 13: cargo tank washing
• MARPOL Annex II regulation 15: cargo record book
• MARPOL Annex II regulation 16: measures of control
• MARPOL Annex II regulation 17: shipboard marine pollution emergency plan
• MARPOL Annex II regulation 18: reception facilities
• The IGC Code
• The IMSBC Code
• SOLAS chapter VII: carriage of dangerous goods
• Marine cargo tank heating systems
• Marine vapor recovery and VOC management
• Tanker size classes
• The STCW Convention