IMDG Class 8: Corrosive Substances Guide

Class 8 of the IMDG Code covers substances that destroy living tissue by chemical action or, on leakage, materially damage other goods or the means of transport. The IMDG segregation calculator and the IMDG packing group calculator are the primary computational tools for Class 8 cargo handling; the full regulatory framework is laid out below.

Regulatory framework and mandatory status

The IMDG Code 2022 Edition, Amendment 41-22, is the operative instrument for sea carriage of packaged dangerous goods. It became mandatory on 1 January 2024 under SOLAS Chapter VII Regulation 3, with voluntary application permitted from 1 January 2023. SOLAS Chapter VII Regulation 1 defines “dangerous goods” and incorporates the IMDG Code by reference; Regulation 3 makes compliance mandatory for all ships on international voyages carrying packaged dangerous goods. The SOLAS Chapter VII article covers that framework in detail.

The IMDG Code draws its classification criteria from the UN Recommendations on the Transport of Dangerous Goods (Model Regulations), currently in its 23rd Revised Edition, and from the UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS, 10th Revised Edition). Class 8 criteria under IMDG Chapter 2.8 align with GHS Category 1 skin corrosion (UN GHS Chapter 3.2) and with the UN Model Regulations Class 8 definition. That alignment means a substance classified as GHS skin corrosion Category 1 with a sub-category mapping to full-thickness destruction times below 4 hours will typically be Class 8 under the IMDG Code, though the IMDG Code has its own specific assignment criteria.

Amendment 41-22 introduced several Class 8 changes relative to the prior 40-20 amendment: revised entries for certain amine mixtures, updated special provisions for corrosive battery entries, and alignment of the Dangerous Goods List (DGL) with the 22nd revised edition of the UN Model Regulations. Any shipper working from printed copies of the 40-20 amendment must verify the DGL entries against the 41-22 edition before the mandatory date.

For bulk carriage of noxious liquid substances (which include many acids and caustics), the governing instrument is MARPOL Annex II read with the IBC Code. The IBC Code article covers bulk chemical carriage. The IMDG Code governs only packaged goods.

Class 8 definition and classification criteria

The two-limb definition

IMDG Code Chapter 2.8.1 states the Class 8 definition in two limbs:

1. Substances that, by chemical action, cause severe damage when in contact with living tissue.
2. Substances that, on leakage, materially damage other goods or the means of transport.

Both limbs are Class 8. A substance can qualify under either or both. The first limb is tested by UN Test C.1 (skin corrosion on rat skin or the reconstructed human epidermis Episkin model); the second by UN Test C.2 (corrosion rate on steel and aluminium). Many strong inorganic acids satisfy both: sulphuric acid destroys skin rapidly and corrodes mild steel at rates far exceeding 6.25 mm per year. Certain metal-organic compounds satisfy only the second limb: they corrode steel aggressively but have limited skin reactivity. Either way, the cargo is Class 8 and attracts all Class 8 requirements.

UN Test C.1: skin corrosion

UN Test C.1 is described in the UN Manual of Tests and Criteria, Part III, Section 37. The test applies the substance to shaved intact rat skin (or the validated in vitro Episkin / EpiDerm / SkinEthic RHE replacement) for a defined exposure period, then examines the site at 14 days (in vivo) or 3 minutes / 1 hour / 4 hours (in vitro). Full-thickness skin destruction (destruction of the epidermis and dermis) within the observation period is the positive result. The three packing group exposure thresholds map directly to this test: 3 minutes for PG I, 1 hour for PG II, and 4 hours for PG III.

In vitro methods under UN Test C.1 have largely replaced the in vivo rat test under animal-welfare pressure. The Episkin and similar validated models use reconstructed human epidermis, and their results correlate well with the in vivo data for most inorganic acids and alkalis. Certain complex organic mixtures still require in vivo confirmation where the in vitro model cannot handle the solubility or pH characteristics.

One practical complication: the corrosion test measures intact skin. Some Class 8 substances (hydrogen fluoride, chromic acid, certain organotin compounds) cause damage through mechanisms that do not manifest as rapid tissue destruction in the first few minutes but produce deep progressive injury over hours. The IMDG classification of these substances reflects their hazard profile, which may result in a PG assignment that appears conservative relative to the 3-minute skin test result alone. Shipboard emergency response for hydrofluoric acid, for example, follows a protocol distinct from the generic Class 8 protocol because of the fluoride ion’s systemic toxicity.

UN Test C.2: metal corrosion rate

UN Test C.2, described in the UN Manual of Tests and Criteria Part III Section 37.4, measures the corrosion rate of the test substance on both SAE 1020 steel and non-clad 7075 aluminium at 55 degrees Celsius over a 7-day test period. The threshold is 6.25 mm per year on either metal. A substance exceeding that rate on steel or aluminium qualifies as Class 8 under the metal-corrosion criterion.

The 6.25 mm/year threshold corresponds to approximately 0.12 mm per week at the 55 degrees Celsius test temperature. At ambient temperatures the corrosion rate will be lower, but the test temperature is set to capture accelerated attack that could damage cargo transport unit (CTU) structure during a prolonged voyage in warm-water service.

An important regulatory nuance: the metal-corrosion criterion assigns Packing Group III only. There is no PG I or PG II assignment based on metal corrosion alone. A substance that has a corrosion rate of 12.5 mm/year on steel but is not corrosive to skin would be PG III, not PG II. The packing group I and II assignments are reserved for skin-destructive substances. This matters for packaging requirements: a highly metal-corrosive substance with no skin effect still gets PG III, with its relatively flexible packaging allowances.

Relationship to GHS and the UN Model Regulations

The UN GHS Chapter 3.2 (Skin Corrosion/Irritation) distinguishes skin corrosion Category 1A (destruction within 3 minutes), Category 1B (destruction within 1 hour), and Category 1C (destruction within 4 hours). These align with IMDG PG I, PG II, and PG III respectively, but GHS Category 1C (IMDG PG III via skin criterion) is not identical to the metal-corrosion-only PG III. GHS does not have a “metal corrosion” category within the skin-corrosion framework; the UN Model Regulations address it under Class 8 separately. Classification authorities reviewing a new substance must check both pathways.

Packing groups: criteria and comparative table

The three packing groups determine packaging rigor, segregation requirements, and the EmS assignment. The table below summarises the assignment criteria and selected operational consequences.

“Packaging performance level X” means the outer packaging must pass the UN performance tests at the highest drop and stacking loads. IMDG Code Chapter 6.1 sets the performance levels: X corresponds to PG I, Y to PG II, and Z to PG III. A Y-rated container can carry PG I and PG II goods only if the packing instruction specifically permits it; for Class 8 it generally does not.

Packing Group I: substances with extreme skin corrosivity

PG I Class 8 substances destroy full-thickness skin within 3 minutes of contact (with up to 60 minutes observation to confirm). The most commercially significant entries include the following.

UN 2031 Nitric acid, other than red fuming, with more than 70% acid. Nitric acid at high concentration combines corrosive attack with oxidising character; it dissolves most metals through nitric acid oxidation and reacts with organic matter including packaging materials. The IMDG DGL entry for UN 2031 assigns stowage Category D (on deck in closed CTU) for ships carrying the cargo at sea; the container-imdg-class calculator gives the stowage category for any UN number.

UN 2032 Nitric acid, red fuming. Red fuming nitric acid (RFNA) contains dissolved nitrogen dioxide and is a PG I oxidiser and corrosive. It generates toxic nitrogen dioxide fumes at ambient conditions and has special stowage requirements that reflect both the Class 8 and Class 5.1 (oxidising) characteristics.

UN 1790 Hydrofluoric acid, solution, more than 60%. HF at concentrations above 60% is PG I. At lower concentrations (7% to 60%) it is PG II; below 7% it is PG III. The HF molecule penetrates deep tissue and the fluoride ion causes systemic fluoride toxicity, cardiac arrhythmia and death at exposures that may produce only minor surface burns initially. Standard Class 8 first-aid protocols are necessary but not sufficient for HF; calcium gluconate gel must be applied after copious water flushing, and cardiac monitoring is required for any significant exposure.

UN 1052 Hydrogen fluoride, anhydrous. Anhydrous HF is additionally a toxic gas (Class 8 with subsidiary Class 6.1 and sometimes Class 2.3 depending on form). Its vapour pressure at ambient temperature makes confined-space exposure potentially lethal within minutes. The IMDG DGL for UN 1052 carries multiple special provisions.

UN 1831 Sulphuric acid, fuming (oleum). Oleum is a solution of sulphur trioxide in concentrated sulphuric acid. It reacts violently with water, releasing heat and dense sulphur dioxide / sulphuric acid mist, and it is PG I. Tank container carriage uses a T22 portable tank minimum. Carbon steel tanks are paradoxically compatible with oleum (the high-concentration passivation film) but not with dilute sulphuric acid.

UN 1732 Antimony pentafluoride. A less-common but important entry: antimony pentafluoride fumes aggressively in moist air and reacts with water to release HF. It is PG I with Class 6.1 and 8 dual hazard.

Packing Group II: the workhorse industrial acids and alkalis

PG II substances destroy skin between 3 minutes and 1 hour. This is the most commercially significant segment: most industrial acid and caustic shipments in drums and IBCs fall here.

UN 1789 Hydrochloric acid (muriatic acid). The standard 30-35% aqueous solution of hydrogen chloride is PG II. It generates hydrogen chloride vapour (immediately detectable as strong, pungent irritant) even at ambient temperatures, so under-deck stowage requires ventilation. It corrodes most metals except certain stainless-steel grades and tantalum.

UN 1823 Sodium hydroxide, solid. Caustic soda in flake, bead or pellet form is PG II. It reacts exothermically with water and can cause ignition of combustible material if the heat of dissolution is large enough. Moisture entry into a drum of NaOH can rupture the drum if the vent is blocked.

UN 1824 Sodium hydroxide solution. The liquid form of caustic soda, typically 30-50% concentration. PG II. Commonly shipped in IBC (intermediate bulk containers) or tank containers.

UN 1813 Potassium hydroxide, solid. Caustic potash, similar in behaviour to NaOH but denser and slightly more reactive. PG II.

UN 2031 Nitric acid, other than red fuming, 65% or less. At concentrations between 20% and 65%, nitric acid is PG II rather than PG I. At less than 20%, it may not meet Class 8 criteria at all depending on specific test data.

UN 1805 Phosphoric acid solution, 85% or less. Ortho-phosphoric acid at high concentration is PG II. Phosphoric acid has the practical advantage of being one of the milder mineral acids in terms of vapour generation: it does not produce a significant acid mist at ambient conditions.

UN 1830 Sulphuric acid, more than 51%. Sulphuric acid at concentrations above 51% is PG II (not PG I). Below 51% it shifts to PG III (UN 2796, battery acid). Above about 93% it is UN 1831 (fuming) territory. The 51% boundary matters operationally: a single shipment of battery acid in drums requires PG III packaging; a shipment of industrial sulphuric at 65% requires PG II packaging.

Packing Group III: lower hazard corrosives and metal-corrosive substances

PG III substances meet either the 1-4 hour skin destruction window or the metal-corrosion rate criterion only. The corrosion-rate-only entry point is exclusively PG III.

UN 2796 Battery acid, sulphuric acid with not more than 51% acid. Dilute sulphuric acid, as used in lead-acid batteries, is PG III. It is one of the most commonly shipped Class 8 goods by shipment count because forklift batteries, UPS batteries and similar equipment travel in service.

UN 2794 Batteries, wet, filled with acid (electric storage battery). The entire battery (not just the electrolyte) is classified under this entry when the battery is transported as cargo. The classification of wet-cell batteries has its own special provisions in the IMDG DGL (Special Provision 238 and others) covering battery size, state-of-charge, and whether the battery is installed in equipment.

UN 1779 Formic acid, more than 85%. Formic acid at high concentration is PG II; between 10% and 85% it is PG III. Below 10% it may not classify as Class 8.

UN 2789 Acetic acid, glacial or acetic acid solution, more than 80%. Glacial acetic acid (essentially anhydrous) is PG II, but acetic acid solutions above 80% are PG III. Below 80% the cargo may not classify as Class 8 depending on concentration. The flammability of acetic acid (flash point 39 degrees Celsius) adds a subsidiary Class 3 hazard for certain concentration ranges.

UN 1715 Acetic anhydride. PG II under the IMDG DGL. Reacts with water to form acetic acid; spill response must account for the exothermic hydrolysis.

Corrosion-rate-only PG III entries. Several substances with corrosion rates exceeding 6.25 mm/year on steel are PG III solely because of the metal-attack criterion. Examples include certain ammonium fluoride solutions, some metal-cleaning preparations, and certain electroplating bath preparations. These carry Class 8 placards and require Class 8 documentation even though their skin-contact hazard may be relatively low.

Stowage categories under IMDG Chapter 7

Category assignments and what they mean

IMDG Code Chapter 7.1 defines five stowage categories:

• Category A: on deck or under deck.
• Category B: on deck or under deck. When under deck, in a mechanically ventilated cargo space.
• Category C: on deck only.
• Category D: on deck only in closed cargo transport unit.
• Category E: on deck only in a closed CTU, in a mechanically ventilated cargo space on passenger ships.

Most Class 8 PG II and III entries fall into Category A or B. Many PG I entries, and entries with subsidiary hazards (oxidising, toxic), move to Category C or D. The specific category for every entry is listed in the IMDG Dangerous Goods List Column 16a and 16b. The container-imdg-class calculator looks up the category directly from the UN number.

Stowage categories interact with ship type. On a passenger ship, an entry that is Category A on a cargo ship may be Category E on a passenger ship (on deck only, in closed CTU, in ventilated space). IMDG Code Chapter 7.1.2 sets out the passenger-ship uplift rules: six specific categories apply to passenger ships, and a substance that is “Category A cargo ship / Category E passenger ship” cannot be stowed under deck on a passenger ship regardless of container type.

Specific stowage requirements for Class 8 in Chapter 7.3

Beyond the stowage category, IMDG Chapter 7.3 lists specific stowage requirements coded SW1 through SW35 and beyond. Class 8 commonly attracts:

• SW1: away from living quarters.
• SW2: protected from sources of heat.
• SW5: stow “separated from” foodstuffs (see also the foodstuff segregation in Chapter 7.2).
• SW22: stow away from accommodation spaces and away from air intakes for PG I acid vapour-generating entries.

The imo-imdg calculator consolidates stowage code lookups for any UN entry.

Ventilation and drainage

Under-deck stowage of liquid Class 8 requires consideration of vapour control. Strong acids (hydrochloric, nitric) generate acid vapour at ambient temperature. IMDG Code Chapter 7.1.7 requires that cargo spaces carrying packages emitting flammable or toxic vapours be mechanically ventilated. For Class 8 acids that emit toxic (or corrosive) vapour, the practical requirement on many ships is at least six air changes per hour in the cargo hold.

Hold drainage and bilge protection matter. A Class 8 acid leak into the bilge will corrode the bilge area, attack the bilge pump, and potentially corrode through the ship’s bottom plating if the drain passages are not acid-resistant lined. Class rules (from class societies) and flag state requirements on chemical tankers specify bilge coatings; for general cargo ships, the IMDG Code’s requirement to prevent cargo space contamination from leaking Class 8 is enforced by port state control through cargo condition inspections.

Segregation under IMDG Chapter 7.2

Reading the segregation table

IMDG Code Chapter 7.2 contains the segregation table. It lists interactions between all class pairs on a grid, using four levels of separation:

• “Away from”: some physical separation, not in the same compartment or hold.
• “Separated from”: in a different compartment or hold.
• “Separated by a complete compartment or hold from”: a structural division between them.
• “Separated longitudinally by an intervening complete compartment or hold from”: not only a structural division but a longitudinal one.

Class 8 has the following key segregation requirements in the IMDG 41-22 table:

The segregation group SG17 (“acids”) and SG18 (“alkalis”) appear in the IMDG DGL for many Class 8 entries. Segregation group SG17 and SG18 interact under Chapter 7.2.8: acids and alkalis must be “separated from” each other. An acid-alkali contact causes a neutralisation reaction that is exothermic, can rupture packaging from gas evolution, and can raise local temperatures above the flash point of any organic component in a mixed cargo load.

Cyanide and sulphide: the lethal interaction pairs

Two specific interactions with Class 8 acids demand attention above all others. Acid contact with any cyanide (inorganic cyanide salts such as sodium cyanide UN 1689, potassium cyanide UN 1680, or hydrogen cyanide itself) produces hydrogen cyanide gas. HCN has an immediately dangerous to life and health (IDLH) concentration of 50 ppm; a single drum of acid leaking onto a drum of solid cyanide in a closed hold could generate a lethal HCN concentration within minutes. The IMDG segregation requirement “separated longitudinally by an intervening complete compartment” reflects this: even “separated by a complete compartment” is considered insufficient for this interaction.

Acid contact with sulphide (sodium sulphide UN 1849, ammonium sulphide solutions) produces hydrogen sulphide. H2S is both a respiratory toxicant and a flame, with an IDLH of 50 ppm and a lower explosive limit of 4.3% by volume. The IMDG segregation calculator implements these pair-specific requirements from the 41-22 segregation table.

Container-to-container application on containerships

On a containership, the segregation rules apply between cargo transport units (CTUs). “Separated from” typically means the two containers must not be in the same hold or bay; “separated longitudinally” means they must be separated by at least one full bay in the longitudinal direction. The exact application depends on ship type and hold configuration; IMDG Code Chapter 7.2.3 to 7.2.6 sets out the containership-specific interpretation.

Multimodal transport adds complexity: a container that moves by road, rail and sea must satisfy the segregation rules at each mode. For sea carriage, the IMDG table applies; for road carriage, ADR Chapter 7.5; for rail, RID. In practice, the sea leg’s IMDG requirements tend to be the binding constraint for acid shipments because the voyage duration and hold configurations are the most restrictive.

Emergency response: EmS schedules and MFAG

Emergency schedules in the IMDG EmS Guide

The EmS Guide provides fire (F-) and spillage (S-) schedules for every DGL entry. Class 8 standard assignments:

F-A (fire schedule A): use water spray. F-A applies to non-flammable Class 8 substances in combustible packaging. Most strong inorganic acids and alkalis are not themselves flammable; the fire is a packaging fire. Water spray cools the packaging and prevents spread. However, water directly on a concentrated acid spill can cause violent spattering as the heat of dilution vaporises the water. The F-A guidance distinguishes the fire-fighting approach (water spray on surrounding cargo and structure) from the spill-response approach.

F-E (fire schedule E): do not use water. Some Class 8 entries that have water-reactive character (concentrated sulphuric acid reacts with water exothermically; oleum reacts very violently) may be assigned F-E. Always check the DGL column for the specific UN number, not only the class.

S-B (spillage schedule B): small spillage. Contain the spill with dry sand or inert absorbent (NOT organic absorbent with strong oxidising acids). For acid spills: neutralise carefully with dilute soda ash or lime, avoiding violent effervescence. For alkali spills: dilute with water and neutralise with dilute acid. Collect the neutralised material into salvage containers for disposal ashore. Wash residual with water. Small spills (under 1 litre from a package) typically use S-B.

S-C (spillage schedule C): large spillage. The same principles as S-B but at larger scale. S-C specifies that mechanical ventilation must be running, personnel must wear SCBA and full acid-resistant suits, and the response team must use pH paper to confirm neutralisation before declaring the area clear. Large spills (a leaking IBC, a ruptured tank container, or a hold contaminated with drum spillage) use S-C.

The specific EmS code for each UN entry is listed in the DGL Column 17. The IMDG EmS lookup calculator retrieves the code and the corresponding schedule text for any UN number.

MFAG guidance for Class 8 casualties

The Medical First Aid Guide (MFAG, IMO publication), available as part of the IMDG Code package, provides first-aid instructions for shipboard casualties involving dangerous goods. MFAG Table 1 lists substances by UN number with chemical name and cross-references to MFAG treatment schedules. For Class 8:

Skin contact (acid): Remove contaminated clothing. Flush with copious water for at least 15 minutes. Do not apply neutralising agents directly to the burn (the neutralisation reaction is exothermic and worsens the injury). Cover with a clean dry dressing. Seek medical attention for all but the most trivial exposures. For hydrofluoric acid, apply 2.5% calcium gluconate gel immediately after water flushing, and continue applying as long as pain persists, because the fluoride ion migrates through tissue and causes continuing destruction long after surface acid is removed.

Skin contact (alkali): Remove contaminated clothing. Flush with copious water for at least 20 minutes (alkali penetration tends to continue longer than acid penetration because saponification of tissue lipids keeps the reaction going). Do not attempt to neutralise with acid. Cover and seek medical attention.

Eye contact: Irrigate immediately with clean water for at least 15 minutes, holding the eyelid open. Alkali eye injuries require ophthalmic follow-up because alkali continues to penetrate the cornea after surface contamination is removed.

Inhalation (acid vapour): Remove to fresh air. If the casualty is breathing but distressed: rest, warmth, oxygen if available. If breathing stops: cardiopulmonary resuscitation. Pulmonary oedema from acid vapour inhalation (hydrogen chloride, nitric acid fumes, sulphur dioxide from oleum) may present with a delay of 4-24 hours; medical evacuation is required even if the casualty appears recovered.

Emergency contact: The 24-hour emergency contact required on the Dangerous Goods Declaration connects the ship’s officer to chemical-specific expertise. For HF incidents, the MFAG explicitly recommends contacting a poison control centre and not relying solely on general corrosive protocols.

Packaging requirements under IMDG Code Chapters 4-6

General packaging principles for Class 8

IMDG Code Chapter 4.1 sets out the packaging instructions for each UN entry. Three packaging instructions cover the bulk of Class 8 liquid entries:

• P001: large variety of drum and jerry-can types in glass, steel, aluminium, plastics, or fibre. Permitted inner packaging types vary by packing group.
• P010: specific entry for UN 1790 hydrofluoric acid (no glass containers because HF etches glass).
• IBC02, IBC03: for intermediate bulk containers carrying Class 8 liquids.

The packaging compatibility requirement in IMDG Chapter 4.1.1.3 prohibits packaging materials that react with the contents. Glass or earthenware containers are prohibited for HF. Aluminium containers are prohibited for alkalis (sodium hydroxide attacks aluminium, forming sodium aluminate and releasing hydrogen). Steel is prohibited for many halogenated acids. The shipper’s technical data sheet must confirm packaging material compatibility, and this information must be available to the carrier.

Intermediate bulk containers (IBCs) for Class 8

IBC use for Class 8 is permitted under the IBC instructions in IMDG Chapter 4.1.4. The table of permitted IBC types for Class 8 specifies:

• Metal IBCs (11A, 11B, 11N): permitted for many PG II and III entries. 11A (steel) for alkalis; 11B (aluminium) NOT for alkalis; 11N (other metal, such as stainless steel) for acids where steel is unsuitable.
• Rigid plastic IBCs (31A, 31H): permitted for many Class 8 entries. HDPE (high-density polyethylene) is compatible with most dilute mineral acids and caustics. Concentrated oxidising acids (nitric acid above 65%, oleum) cannot use HDPE IBCs because the material degrades and eventually fails.
• Composite IBCs (31HZ1): inner plastic container in an outer metal or rigid plastic casing. Widely used for PG II Class 8 liquids.

PG I entries restrict IBC use more severely: many PG I acids cannot use IBCs at all (they require UN-certified drums or tank containers). This is a common shipper error: using an IBC-rated for PG II to carry a PG I cargo is a non-conformity that creates both regulatory exposure and genuine safety risk.

Tank containers: T-codes and the portable tank instruction

IMDG Code Chapter 4.2 governs portable tanks (tank containers). Each UN entry in the DGL has a column specifying the portable tank instruction (T1 through T23) and any special provisions (TP1 through TP44).

For Class 8, the key T-code assignments are:

• T1: the lightest requirement. Minimum test pressure 1.5 bar, no special wall requirements. Not applicable to strong acids.
• T7: minimum test pressure 4 bar. Used for PG III dilute acids and caustics.
• T11: minimum test pressure 4 bar, with a bottom outlet exception. Used for many Class 8 PG II entries.
• T14: minimum test pressure 4 bar, with additional structural requirements. Used for concentrated sulphuric acid (UN 1830) and other PG II strong acids.
• T20: minimum test pressure 6 bar. Used for several PG I entries.
• T22: minimum test pressure 6 bar with no bottom outlets. UN 1831 (oleum) and UN 1052 (anhydrous HF) are T22.

Construction materials for Class 8 tank containers:

Stainless steel 316L is the material of choice for most mineral acids (hydrochloric, phosphoric, dilute sulphuric). It has an acceptable corrosion rate in dilute mineral acid service but is not suitable for hydrofluoric acid (HF attacks the passive chromium-oxide film on stainless steel). Hastelloy C-276 (a nickel-molybdenum-chromium alloy) is used for HF service. Carbon steel is used for oleum (the passivation film formed by high-concentration sulphuric acid protects carbon steel; water would dissolve that film so strict dryness is required). PTFE-lined tanks are used for the most aggressive species where metallic construction is impractical.

Material mismatches between cargo and tank are documented causes of incidents. The imdg-tank-container calculator matches UN number to permitted T-code and flags construction requirements.

Limited quantities and excepted quantities

Class 8 goods in consumer-oriented small packages can use the limited quantity (LQ) scheme under IMDG Chapter 3.4. The LQ inner quantity limit for Class 8 ranges from 0 mL (prohibited) for certain PG I entries to 1 L for many PG II liquids to 5 L for many PG III liquids. The LQ mark (a square-on-corner diamond with “Y” inside) replaces the full Class 8 placard and label requirements.

The excepted quantity (EQ) scheme under IMDG Chapter 3.5 allows even smaller quantities (typically less than 30 mL or 30 g for E1 through E4 codes) with minimal marking. Many Class 8 PG III substances have an EQ code E1 or E2. EQ shipments do not need a Dangerous Goods Declaration. The imdg-limited-quantity calculator checks LQ and EQ eligibility and the applicable marks.

Marine pollutant designation and MARPOL Annex III

Which Class 8 entries are marine pollutants?

MARPOL Annex III, implemented through IMDG Code Appendix B, lists substances harmful to the marine environment (HME) that must be marked with the marine pollutant mark when shipped in packages. Many Class 8 substances qualify: strong mineral acids acidify receiving water (a pH effect that MARPOL Annex III does not capture well, since the category is defined by ecotoxicology rather than pH), but heavy-metal-containing solutions and certain organometallic corrosives are listed as marine pollutants.

The DGL column for “Marine Pollutant” (P) and “Severe Marine Pollutant” (PP) is the reference. Examples from Class 8:

• UN 1758 Chromic acid solution: marine pollutant (chromium VI is toxic to aquatic organisms).
• UN 1782 Hexafluorophosphoric acid: not a marine pollutant.
• UN 1809 Phosphorus trichloride: marine pollutant.
• UN 1823/1824 Sodium hydroxide: not listed as a marine pollutant (high pH is harmful but dilution in the marine environment is rapid and reversible).

For marine pollutant entries, the package must carry the marine pollutant mark (a fish over a dead tree) in addition to the standard Class 8 label. The marpol-iii-marine-pollutant-lookup calculator and the marpol-annex3-packaging calculator support MARPOL Annex III compliance for Class 8 consignments. The MARPOL Annex III article covers the Annex III framework in detail.

Marking, labelling, and placarding

The Class 8 label

The Class 8 hazard label is the “corrosive” diamond: a black corrosive action pictogram (a hand and a bar of metal being attacked by liquid drops, against a white background with a black bottom half) with the class number “8” in the lower corner. Under IMDG Code Chapter 5.2, the label must be at least 100 mm by 100 mm on packages.

For mixed loads, additional subsidiary-hazard labels are required alongside the Class 8 label. For example, acetic acid (which is both corrosive and flammable) carries both the Class 8 label and the Class 3 flammable-liquids label. The IMDG DGL Column 4 lists all subsidiary risks for each entry.

Placarding on cargo transport units

Under IMDG Code Chapter 5.3, a CTU (container, vehicle, wagon) carrying Class 8 must be placarded on all four sides with the Class 8 placard (same diamond design as the label but enlarged to 250 mm by 250 mm). Where the CTU carries multiple IMDG classes, all applicable placards appear. Limited-quantity and excepted-quantity shipments may be exempt from CTU placarding under the conditions in Chapter 5.3.1.4.

For dangerous goods in bulk (not applicable to Class 8 packed goods, which use IMDG, but noted for comparison), IMSBC code placarding rules apply instead. The IMDG marking, labelling and placarding article covers the full placarding requirements across all IMDG classes.

Dangerous Goods Declaration and documentation

Mandatory document content

IMDG Code Chapter 5.4 sets the mandatory content of the Dangerous Goods Declaration (DGD) or multimodal dangerous goods form. For Class 8 consignments, the mandatory elements are:

1. UN number in the format “UN XXXX”.
2. Proper shipping name from the IMDG DGL (not a trade name). For Class 8, the proper shipping name often includes the concentration: “Sulphuric acid with more than 51% acid” not “sulphuric acid”.
3. Primary hazard class: “8”.
4. Packing group: “I”, “II”, or “III” (written in Roman numerals or with “PG” prefix: “PG I”).
5. Number and type of packages, net quantity.
6. Total net weight or volume.
7. Marine pollutant if applicable: “MARINE POLLUTANT” or “ENVIRONMENTALLY HAZARDOUS”.
8. EmS codes: listed in many conventions’ DGD forms, though the IMDG Code Chapter 5.4.3 does not make them a mandatory DGD element; carriers often require them.
9. 24-hour emergency contact for the consignor.
10. Consignor’s declaration: the goods are declared as classified, packed, marked, and labelled in accordance with the IMDG Code.

A common documentation error for Class 8: failing to state the concentration when the proper shipping name requires it (as for sulphuric acid, nitric acid, and several other concentration-dependent entries). A Dangerous Goods Declaration that says only “Sulphuric acid, Class 8, PG II” without the concentration cannot be verified against the classification criteria and is non-conforming.

Cargo Transport Unit (CTU) packing certificate

IMDG Code Chapter 5.4.2 requires a CTU packing certificate (Container/Vehicle Packing Certificate) for cargo transport units carrying dangerous goods. The certificate must confirm that:

• The CTU is fit for purpose and the inside is clean, dry, and free of residue incompatible with the cargo.
• The cargo has been stowed and secured in accordance with IMDG Chapter 5.4.2 and CTG Code (the Code of Practice for Packing of Cargo Transport Units).
• For Class 8 in drums: drum bungs are tight; drums are stacked within their own rated stacking weight; drums are oriented with bungs upright; overpacks or pallets are not stacked higher than the IBC or drum manufacturer’s rating.
• Placards and marks are applied to the outside of the CTU.

The CTG Code (jointly published by IMO, ILO, and UNECE) provides the detailed packing guidance for CTUs. It specifies anti-tip protection for drums of PG I Class 8, the maximum stack height for IBCs of different ratings, and the blocking and bracing requirements for tank containers.

Interaction with Classes 3, 4, 5, and 6.1

Class 8 corrosives interact with several other IMDG classes in ways that produce secondary hazards more dangerous than either substance alone. This article focuses on Class 8 specifically; the interaction partners are covered in detail in the parallel articles for Class 3 flammable liquids, Class 4 flammable solids and reactive substances, and Class 5 oxidisers and organic peroxides.

The three most operationally important interactions:

Acid + cyanide (Class 6.1, toxic and infectious substances). Any acid stronger than carbonic acid (pH below 6.35) decomposes cyanide salts to HCN gas. In a ship’s hold, even a minor acid leak reaching a sodium cyanide container can generate a lethal HCN concentration. The LC50 of HCN for humans is approximately 100-300 ppm for a 30-minute exposure; concentrations at the positive exit of a closed hold could reach those levels rapidly. For this reason the segregation requirement is the most stringent in the IMDG table: separated longitudinally by an intervening complete compartment.

Acid + hypochlorite or oxidising agent (Class 5.1). Strong acid reacting with sodium hypochlorite (bleach, UN 1791) produces chlorine gas. Chlorine has an LCLO of 500 ppm in a 30-minute exposure (US NIOSH data). The reaction is immediate and the gas is dense (2.5 times the density of air), so it fills the cargo hold from the bottom.

Concentrated nitric acid (UN 2031, Class 8) + organic material. Fuming nitric acid (UN 2032) and concentrated nitric acid react with many organic materials (wood, cotton, cardboard) to cause ignition or fire. This is the reason for the stowage “separated from organic materials” special provision on several nitric acid entries. A cargo of nitric acid drums in direct contact with palletised organic goods creates an incipient fire risk before any formal breach of segregation occurs.

Limitations

This article describes Class 8 classification, packaging, stowage, segregation, and documentation as set out in the IMDG Code 2022 Edition, Amendment 41-22, mandatory from 1 January 2024. Several caveats apply:

The IMDG Code is revised every two years on an alternating-amendment schedule. Amendment 43-26 will supersede 41-22. Specific UN entries, special provisions, and packaging instructions change between amendments. Always verify the Dangerous Goods List entry in the current operative edition for the specific UN number being shipped.

National implementing legislation can add requirements beyond the IMDG Code minimum. Port state controls in the European Union, the United States, and Australia have each imposed additional Class 8 requirements in port-specific directions and national regulations (such as US 49 CFR Part 173 Subpart D for domestic US shipments of corrosives). A consignment that meets IMDG requirements may face additional inspection requirements in specific ports.

The skin-corrosion test (UN Test C.1) and the metal-corrosion test (UN Test C.2) produce packing group assignments for pure substances and simple mixtures. For complex chemical mixtures (multi-component industrial preparations, reaction products), the classification authority may require actual test data rather than calculated values. The IMDG Code Chapter 2.8.3 allows calculation of mixture classification only under defined conditions; outside those conditions, testing is required.

HF-specific protocols (calcium gluconate, systemic monitoring, medical evacuation for significant exposure) are not fully captured by the generic Class 8 MFAG guidance. Shipboard response plans for vessels regularly carrying HF should include a vessel-specific HF emergency response procedure cross-referenced to the MFAG.

Transport by sea in tank containers imposes additional regulatory layers: the tank must be type-approved by a recognised body (IACS class society for portable tanks), the periodic testing requirements of IMDG Code Chapter 6.7 apply (2.5-year and 5-year hydraulic tests), and the consignor must ensure the tank is within its validity period. A tank container with an expired test certificate is non-conforming regardless of the cargo classification.

This article does not cover the carriage of Class 8 substances in bulk (chemical tankers, IBC Code), which is regulated by MARPOL Annex II and the IBC Code rather than the IMDG Code.

See also

• IMDG Class 1: Explosives
• IMDG Class 2: Gases
• IMDG Class 3: Flammable Liquids
• IMDG Class 4: Flammable Solids
• IMDG Class 5: Oxidisers and Organic Peroxides
• IMDG Class 6: Toxic and Infectious Substances
• IMDG Class 9: Miscellaneous Dangerous Goods
• IMDG Marking, Labelling and Placarding
• SOLAS Chapter VII: Carriage of Dangerous Goods
• MARPOL Annex III: Harmful Substances in Packaged Form
• IBC Code
• IMDG Segregation Calculator
• IMDG Packing Group Calculator
• IMDG EmS Lookup
• Container IMDG Class Lookup
• IMDG Limited Quantity Calculator
• Tank Container T-Code Calculator
• IMO IMDG Calculator
• MARPOL Annex III Marine Pollutant Lookup
• MARPOL Annex III Packaging Calculator
• IMDG Packing Group from Flash Point