IMDG Class 3: Flammable Liquids Guide

What Class 3 covers

Class 3 is the IMDG Code designation for flammable liquids: substances whose vapour will ignite when exposed to an ignition source at or near ambient temperature. The class is the largest by shipment count on container vessels and the most commonly encountered by deck officers at general cargo ports.

The definition in IMDG Code 41-22 Chapter 2.3.1 is precise. A liquid is Class 3 if it meets one of three criteria. First, it has a closed-cup flash point at or below 60 degrees C. Second, it is a liquid transported or offered for transport at a temperature at or above its flash point (elevated-temperature transport). Third, it is a viscous substance whose flash point is above 60 degrees C but not more than 100 degrees C and which, by virtue of viscosity, does not sustain combustion when tested by the sustained-combustibility test in the UN Model Regulations Chapter 32, Section 32.4. That third category is the “viscous-substance exception” and it captures substances such as heavy fuel oil blends and bituminous mixtures that are technically above the 60 degrees C threshold but still meet the Class 3 criteria by failing the sustained-combustibility test.

The 60 degrees C closed-cup threshold is not arbitrary. The UN Model Regulations trace it to the point at which vapour generation at ambient temperature is sufficient to form an ignitable mixture above the liquid surface without external heating. A liquid with a flash point of 55 degrees C generates ignitable vapour on a warm summer deck at 35 degrees C air temperature with little difficulty. A liquid with a flash point of 65 degrees C requires active heating of the bulk before ignitable vapour concentrations develop. The threshold therefore marks the practical boundary between cargoes requiring fire-prevention controls during normal maritime handling and cargoes that are hazardous only under abnormal conditions.

The flash point test and how it works

Flash point is measured by the closed-cup method for all Class 3 classification purposes. The test method matters because open-cup and closed-cup results for the same liquid can differ by 5 to 15 degrees C, with the open-cup reading higher.

The primary methods referenced in the IMDG Code and in the UN Model Regulations are the Pensky-Martens closed-cup test (ISO 2719 / ASTM D93), used for liquids with a flash point above approximately 40 degrees C, and the Abel closed-cup test (ISO 13736 / IP 170) or the Tag closed-cup test (ASTM D56), used for lower flash points. All three methods seal the test cup, heat the sample at a controlled rate, and introduce a small test flame through a sliding shutter at set temperature intervals. The flash point is the temperature at which the vapour above the liquid ignites momentarily (a “flash”) without sustaining combustion. The ASTM D93 flash point calculator and the ASTM D7094 modified continuously closed cup calculator support the flash-point computation workflow for these standard methods.

The initial boiling point (IBP) is the second parameter needed to assign a packing group. It is the temperature at which the vapour pressure of the liquid equals atmospheric pressure (101.3 kPa), measured under standard test conditions. For single-component liquids this equals the normal boiling point. For mixtures such as petroleum naphtha, it is the temperature at which the first bubble of vapour forms in the liquid column during a standardized distillation run (ASTM D86 or ISO 3405 for petroleum products). IBP is distinct from the initial distillation temperature in a fractional-distillation run, which is the temperature at which the first drop of distillate condenses in the receiver.

Packing group assignment

The three packing groups (PG) for Class 3 are defined by the combination of closed-cup flash point and initial boiling point. The IMDG Code 41-22 Chapter 2.3.2.1 table is reproduced in simplified form below. The IMDG packing group calculator and the packing group from flash point calculator implement the full decision logic.

Packing group table

PG I captures the most volatile substances. A liquid whose initial boiling point is at or below 35 degrees C is under substantial vapour pressure at normal ambient temperatures, meaning it releases ignitable vapour faster than almost any ventilation or containment measure can dilute it. Diethyl ether (UN 1155, boiling point 34.6 degrees C, flash point minus 45 degrees C), pentane (UN 1265, boiling point 36 degrees C, flash point minus 49 degrees C), and carbon disulfide (UN 1131, boiling point 46 degrees C, flash point minus 30 degrees C) all fall in PG I. Carbon disulfide is unusual: its auto-ignition temperature is only 90 degrees C, meaning a steam pipe or a light bulb surface at full temperature can ignite it without an open flame.

PG II holds the majority of Class 3 cargo by volume. Gasoline (UN 1203, flash point typically minus 40 degrees C, IBP approximately 30 to 40 degrees C depending on grade) is classified PG II because its IBP exceeds 35 degrees C. Ethanol (UN 1170, flash point 13 degrees C, IBP 78 degrees C) is PG II. Acetone (UN 1090, flash point minus 20 degrees C, IBP 56 degrees C) is PG II. Toluene (UN 1294, flash point 4 degrees C, IBP 111 degrees C) is PG II. Methanol (UN 1230, flash point 11 degrees C, IBP 65 degrees C) is PG II with the additional subsidiary risk of Class 6.1 toxic.

PG III covers the middle-flash-point range. Kerosene (UN 1223, flash point 38 to 72 degrees C, IBP approximately 150 degrees C) is PG III. Diesel fuel (UN 1202, flash point typically 52 to 96 degrees C depending on grade – only the portion with flash point at or below 60 degrees C falls in Class 3). Jet fuel Jet A-1 (UN 1863, flash point minimum 38 degrees C, IBP approximately 145 degrees C) is PG III. Isopropanol / isopropyl alcohol (UN 1219, flash point 12 degrees C, IBP 82 degrees C) is PG II despite moderate volatility because its flash point is below 23 degrees C.

The elevated-temperature exception

A substance with a flash point above 60 degrees C enters Class 3 if it is transported at or above its flash point. The most common case is bitumen and some heavy fuel oil blends transported in heated tank containers or tank wagons at 100 to 160 degrees C. The UN number and proper shipping name reflect the elevated-temperature condition, and an additional high-temperature hazard applies (IMDG Code Chapter 3.3, Special Provision 239 covers flash point above 60 degrees C substances transported hot).

Mixtures and blends

For a liquid mixture of defined composition, the flash point and IBP of the mixture determine the classification; they cannot be assumed from the components. For petroleum blends, flash point is measured on the actual sample. Where flash point data is not available for a mixture, the manufacturer or shipper must determine it by testing before classification is declared. Blending two non-Class-3 liquids can produce a Class 3 mixture if one component lowers the flash point of the system (the depression effect in certain aromatic-aliphatic blends).

Class 3 and the Dangerous Goods List

The Dangerous Goods List (DGL) in IMDG Code 41-22 Volume 2 contains over 3,000 entries. Class 3 entries are among the most numerous. The DGL gives, for each UN number: the proper shipping name, class (primary and subsidiary), packing group, special provisions, limited and excepted quantities, packaging instructions, portable tank instruction (T-code), tank container special provisions, EmS codes, stowage category, and segregation group.

Key Class 3 UN entries include:

• UN 1090 ACETONE, Class 3, PG II, stowage category B, EmS F-E/S-E
• UN 1130 CAMPHOR OIL, Class 3, PG III, stowage category A, EmS F-E/S-E
• UN 1131 CARBON DISULFIDE, Class 3 (+ 6.1 subsidiary), PG I, stowage category E (on deck only), EmS F-E/S-E
• UN 1155 DIETHYL ETHER, Class 3, PG I, stowage category E, EmS F-E/S-E
• UN 1170 ETHANOL (ETHYL ALCOHOL) SOLUTION, Class 3, PG II (>24% ethanol) or PG III (varies), stowage category A or B
• UN 1202 DIESEL FUEL / GAS OIL, Class 3, PG III (flash point 23-60 degrees C band only), stowage category A, EmS F-E/S-E
• UN 1203 GASOLINE (PETROL, MOTOR SPIRIT), Class 3, PG II, stowage category B, EmS F-E/S-E
• UN 1219 ISOPROPANOL (ISOPROPYL ALCOHOL), Class 3, PG II, stowage category B, EmS F-E/S-E
• UN 1223 KEROSENE, Class 3, PG III, stowage category A, EmS F-E/S-E
• UN 1230 METHANOL, Class 3 + 6.1 (subsidiary toxic), PG II, stowage category B, EmS F-E/S-E
• UN 1265 PENTANES, liquid, Class 3, PG I, stowage category E, EmS F-E/S-E
• UN 1268 PETROLEUM DISTILLATES (various), Class 3, PG I/II/III depending on flash point
• UN 1294 TOLUENE, Class 3, PG II, stowage category B, EmS F-E/S-E
• UN 1863 FUEL, AVIATION, TURBINE ENGINE (Jet A-1), Class 3, PG III, stowage category A, EmS F-E/S-E
• UN 1993 FLAMMABLE LIQUID, N.O.S. (catch-all entry for unspecified Class 3 mixtures), PG I/II/III per flash point

The IMDG EmS lookup calculator and the container IMDG class lookup cover the full DGL for any UN number.

Stowage categories

The IMDG Code Chapter 7.1 defines five stowage categories (A through E) that prescribe where on a ship dangerous goods may be placed. For Class 3:

Category A (on deck or under deck): acceptable for most PG III cargo, particularly those with flash points above 23 degrees C and no additional acute hazard. Kerosene (UN 1223), diesel in the Class 3 band (UN 1202), and Jet A-1 (UN 1863) typically attract category A. Category A permits under-deck cargo spaces provided that they are equipped with mechanically operated ventilation systems with at least six air changes per hour and that the electrical equipment is of a type approved for flammable-vapour atmospheres.

Category B (preferably on deck): required for PG II cargo with flash points below 23 degrees C where the DGL entry does not mandate category E. Gasoline (UN 1203), toluene (UN 1294), ethanol (UN 1170), and isopropanol (UN 1219) typically attract category B. Under-deck stowage is permitted but the master is expected to prefer on-deck positions to reduce the risk of below-deck vapour accumulation.

Category C (on deck only): not typically a Class 3 requirement in the standard DGL entries. Some Class 3 + subsidiary hazard combinations impose category C by composite.

Category D (under deck only): not standard for Class 3. Certain Class 1 explosives interactions may require Class 3 cargo to be kept away from open-deck positions, but this derives from the segregation rule rather than the stowage category.

Category E (on deck only with additional conditions): applies to the most volatile PG I substances with high vapour pressure. Carbon disulfide (UN 1131), diethyl ether (UN 1155), and pentane (UN 1265) attract category E. On-deck stowage ensures that leaked vapour disperses to atmosphere rather than accumulating in an enclosed space. Category E also restricts the cargo from holds where ventilation cannot guarantee continuous fresh-air purging.

The actual stowage category for any entry should be read from the DGL column 16 for that specific UN number. The general patterns above reflect typical assignments; special provisions in column 10 or 17 can modify them.

Segregation requirements

IMDG Code Chapter 7.2 specifies segregation between classes. Segregation requirements are stated as one of four levels: “away from,” “separated from,” “separated by a complete compartment or hold from,” and “separated longitudinally by an intervening complete compartment or hold from.” Chapter 7.2.4 provides the segregation table, and the DGL columns 16b and 17 give any class-specific or entry-specific deviations.

For Class 3 the principal segregation relationships are:

Class 3 and Class 1 (Explosives): segregation “separated longitudinally by an intervening complete compartment or hold from” for most Class 1 compatibility groups. The flammable vapour / detonation combination is the worst-case scenario for a ship cargo hold.

Class 3 and Class 2.1 (Flammable Gases): “separated from.” Both classes present vapour-ignition hazards, but Class 2.1 gases are already subject to their own containment requirements under the DGL. The same-class-fire-response logic applies: foam is compatible with both.

Class 3 and Class 4.1 (Flammable Solids) / Class 4.2 (Spontaneously Combustible) / Class 4.3 (Water-Reactive): “separated from.” For Class 4.3 the mechanism is more specific: water used to fight a Class 4.3 fire releases flammable hydrogen or acetylene gas, which can ignite from Class 3 vapour already present in the hold. Class 4.2 substances self-heat; adjacent Class 3 vapour converts any ignition into a rapid fire.

Class 3 and Class 5.1 (Oxidizing Substances): “separated by a complete compartment or hold from.” This is the most consequential pairing in everyday container stowage planning. An oxidizer releases oxygen when decomposing or when heated; Class 3 vapour in the presence of excess oxygen at ambient temperature can reach ignitable concentrations at lower vapour pressures than in air. The IMDG segregation calculator implements the full Chapter 7.2 table and the DGL deviations for any UN-number pair.

Class 3 and Class 5.2 (Organic Peroxides): “separated longitudinally by an intervening complete compartment or hold from.” Organic peroxides decompose exothermically when heated; a self-heating peroxide adjacent to Class 3 vapour produces conditions for a vapour cloud explosion.

Class 3 and Class 8 (Corrosives): “separated from” for most entries. Some Class 3 substances with secondary corrosive hazard (e.g., flammable corrosive liquids) have a combined entry covering both risks; the stowage category and segregation for those entries reflects the more demanding of the two requirements. The sibling article IMDG Class 8: Corrosive Substances covers the Class 8 side of the interface.

Class 3 and Class 4 (Flammable Solids, Spontaneously Combustible, Water-reactive): the sibling article IMDG Class 4: Flammable Solids covers the Class 4 side of the interface.

Class 3 and Class 5 (Oxidizers): the sibling article IMDG Class 5: Oxidisers and Organic Peroxides covers the Class 5 side.

Subsidiary risks and combined classifications

Class 3 is the primary class when flammability is the dominant hazard. Several common Class 3 substances carry a subsidiary hazard that modifies packaging, placarding, and documentation.

Class 3 + 6.1 (toxic): methanol (UN 1230) is the highest-volume example. The DGL entry assigns Class 3 primary with Class 6.1 subsidiary, PG II. The package carries both the Class 3 flame label and the Class 6.1 skull-and-crossbones label. The dangerous goods declaration must show both classes. The EmS schedules are those for the primary class (F-E, S-E for UN 1230), but the medical first-aid guide reference is MFAG Table 2 (toxic substances) rather than Table 17 (flammable liquids) because the toxic hazard to the crew is the dominant secondary concern in a spillage scenario.

Class 3 + 8 (corrosive): flammable corrosive liquids such as allyl chloroformate (UN 1722) carry both the flame and the corrosive-liquid labels. The stowage category and segregation from incompatibles applies the stricter of the two class requirements.

Class 3 + 6.1 + 8 (three-hazard entries): relatively rare, but dimethyl sulfate (UN 1595) carries Class 6.1 primary with Class 3 and Class 8 subsidiary. The hierarchy follows PG determination on the basis of the most dangerous primary hazard.

The IMDG packing group calculator handles multi-hazard entries and returns the correct PG for the primary class.

Packaging requirements

IMDG Code Chapter 4 specifies packaging instructions for each DGL entry. Class 3 packaging instructions depend on the packing group.

Drums and jerricans: the standard for small-to-medium volumes.

• PG I: UN-certified combination or single packagings, typically P001 (for packagings) or LP01 (for large packagings). Maximum net mass per package is limited by UN-test certification of the specific packaging type.
• PG II: P001 or LP01. Same structure, but the UN certification test pressures and drop-test heights are lower than PG I.
• PG III: P001 for packagings; the test criteria are the least demanding.

Intermediate Bulk Containers (IBCs): for volumes of 0.45 to 3.0 m3. Class 3 IBC instruction is IBC02 (for PG I/II/III, metal, rigid plastic, composite, and flexible IBCs of appropriate type per the packaging instruction). Metal IBCs (metal rigid body) and rigid composite IBCs (plastic inner with metal or plywood outer) are the most common for PG II flammable liquids. Flexible IBCs are prohibited for PG I. The flash point compliance check calculator verifies whether a specific sample falls within the Class 3 boundary.

Portable tanks (tank containers): the DGL T-code column specifies the portable tank instruction for each UN entry.

• PG I: typically T11 (minimum test pressure 4.0 bar, bottom outlets allowed with defined restrictions per special provision TP7/TP33 where applicable).
• PG II: typically T11 or T7 (minimum test pressure 4.0 bar or 1.75 bar depending on entry).
• PG III: typically T7 (minimum test pressure 1.75 bar, bottom outlets generally permitted).

The IMDG tank container calculator returns the required T-code for any Class 3 UN number. Tank containers for Class 3 must be marked with the UN number in 65 mm high orange plates front and rear, and placarded with the Class 3 diamond on all four sides.

Relationship to SOLAS Chapter II-2 and fire safety

SOLAS Chapter VII Regulation 1 mandates compliance with the IMDG Code for the carriage of dangerous goods in packaged form on all ships. The SOLAS Chapter VII article covers the full regulatory framework. The IMDG Code’s Class 3 stowage requirements dovetail with SOLAS Chapter II-2 fire-protection requirements in two specific ways.

First, SOLAS II-2 Regulation 4.2.1.1 defines “low flash point” cargo as any substance with a flash point below 60 degrees C, which is exactly the Class 3 boundary. Tanks, piping systems, pumps, and transfer equipment for low-flash-point liquids aboard any ship must meet the fire-safety requirements for that category: no open-flame equipment in the adjacent spaces, no non-intrinsically-safe electrical equipment within explosion risk zones, and either water-spray or inert-gas protection for the cargo area.

Second, SOLAS II-2 Regulation 19 (Requirements for ships carrying dangerous goods) requires that cargo ships carrying Class 3 dangerous goods have structural fire protection arrangements, detection and alarm systems, and fire-fighting systems appropriate to the cargo. On container vessels, this is satisfied by the existing fixed gas-detection system in container holds and the CO2 or equivalent fixed fire-suppression system.

The SOLAS II-2 rules apply to ship construction and equipment, not to the cargo classification or the IMDG DGL. A diesel cargo with a flash point of 55 degrees C on a particular batch is Class 3 PG III under IMDG; the same batch loaded in a tanker as bulk MARPOL Annex I cargo is governed by the IBC Code / MARPOL construction rules rather than the IMDG Code. The 60 degrees C threshold appears in both regimes but the consequences differ.

Relationship to MARPOL Annex III and the marine pollutant designation

Many Class 3 substances are simultaneously marine pollutants under MARPOL Annex III. The designation is determined by the environmental hazard criteria in the UN Model Regulations: bioaccumulation potential, acute aquatic toxicity (EC50 or LC50 below 1 mg/L), and chronic aquatic toxicity under OECD test protocols. MARPOL Annex III applies exclusively to harmful substances carried by sea in packaged form, making it the companion regime to the IMDG Code rather than to MARPOL Annex I (bulk oil) or Annex II (bulk noxious liquids).

Class 3 substances that are marine pollutants include several petroleum distillate fractions (some naphtha fractions with high aromatic content), chlorinated solvents such as methylene chloride (UN 1593, Class 3 PG III + marine pollutant), certain agrochemical solvent carriers, and organometallic flammable compounds. The IMDG DGL flags marine pollutants with the letter “P” in the special provisions column and with the fish-and-tree symbol in the placard column.

Practical consequences of the marine pollutant designation on Class 3 cargo:

1. An additional marine-pollutant label (fish-and-tree symbol) must be affixed to every package and every freight container carrying such cargo, alongside the Class 3 flame diamond.
2. The dangerous goods declaration must include the words “MARINE POLLUTANT” immediately after the UN number and proper shipping name.
3. MARPOL Annex III Regulation 5 requires that such cargo be stowed so as to minimize risk of loss overboard in an emergency. This is generally satisfied by the Class 3 stowage requirements but creates an additional documentation obligation for the master.
4. If the substance is lost overboard, MARPOL Article 8 reporting obligations apply to the flag state and potentially to the coastal state.

Bulk carriage and the limits of IMDG applicability

The IMDG Code covers only packaged cargo. Bulk Class 3 liquids fall outside IMDG. Two parallel regimes cover the dominant bulk Class 3 trades:

MARPOL Annex I covers bulk petroleum products (crude oil, gasoline, naphtha, jet fuel, kerosene, gas oil, diesel, fuel oil). Oil tankers carrying these cargoes are governed by the MARPOL Annex I construction and equipment requirements (oil-tight double bottoms, segregated ballast tanks, inert gas systems, crude-oil washing, etc.) and the IBC Code for any Annex II components in the cargo. The SOLAS Chapter VII regime for packaged goods does not apply to these tanker cargoes.

MARPOL Annex II and the IBC Code cover bulk noxious liquid substances carried by chemical tankers. Methanol, ethanol, MTBE, styrene, and other Class 3 substances that are also “noxious liquid substances” for Annex II purposes are carried under the IBC Code. The chemical tanker’s IBC Code certificate identifies which products the vessel may carry and under what conditions.

The practical consequence is that a shipper moving gasoline in drums on a container vessel uses the IMDG Code (UN 1203, Class 3, PG II). The same gasoline moved in a full cargo parcel on an oil tanker uses MARPOL Annex I. The chemistry is identical; the regulatory regime is determined by the mode of carriage.

EmS schedules: fire and spillage response

The Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide, current edition) assigns fire (F-x) and spillage (S-x) schedules to each DGL entry. The majority of Class 3 entries use F-E and S-E.

EmS F-E: Flammable liquids, fire schedule

EmS F-E applies when a Class 3 package is involved in a fire or is adjacent to a fire. The key actions:

1. Keep away. The first priority is to deny the fire access to additional Class 3 cargo. Move adjacent units if it is safe to do so within the first 60 seconds; after that the thermal radiation makes approach impossible.
2. Foam attack. Foam is the primary extinguishing agent for Class 3 fires. Mechanical foam (AFFF at 3% or 6%, protein foam, film-forming fluoroprotein foam) blankets the liquid surface and suppresses vapour generation. Water jet is contraindicated: it splashes the burning liquid and spreads the fire, and water does not extinguish burning flammable liquid.
3. Boundary cooling with water spray (not jet). Adjacent structures, containers, and bulkheads are cooled with water spray to prevent BLEVE conditions in any tanks or the thermal ignition of adjacent Class 3 units. Water spray on the outer surfaces of containers involved in a fire is also acceptable as a supplementary measure alongside foam.
4. Do not enter the fire zone without breathing apparatus and full fire-fighting equipment.
5. Muster the crew to upwind assembly stations.

EmS S-E: Flammable liquids, spillage schedule

EmS S-E applies when a Class 3 cargo has leaked but has not yet ignited.

1. Eliminate all ignition sources in the area immediately. Switch off non-intrinsically-safe electrical equipment, prohibit smoking, stop any hot-work in adjacent spaces.
2. Contain the liquid. Use sand, vermiculite, expanded clay granules, or proprietary spill-absorbent pads to surround and absorb the spill. Do not wash to drains: the drain leads either to the engine room bilge or to the sea, both of which create secondary hazards.
3. Recover the contaminated absorbent to a salvage drum with a UN-type-certified closure. Label the drum with the UN number of the spilled substance plus the words “SALVAGE.”
4. Ventilate the affected space to atmosphere to disperse residual vapour below the lower flammable limit (LFL). Intrinsically safe forced-ventilation fans must be used; standard bilge fans are not intrinsically safe and their motors can ignite vapour.
5. Monitor vapour concentration with a calibrated combustible-gas indicator. When concentrations fall below 10% of the LFL throughout the space, normal ventilation may resume.

Entries with secondary corrosive hazard use S-D (spillage of corrosive substances) instead of S-E. Check the DGL column 15 for the specific UN number.

The IMDG EmS lookup calculator returns the correct F-x and S-x codes for any Class 3 UN number.

Medical First Aid Guide (MFAG)

The MFAG, published by IMO as a companion to the IMDG Code, provides first-aid instructions for crew members exposed to dangerous goods. Class 3 substances without subsidiary toxic hazard typically reference MFAG Table 17 (flammable substances). The principal concern for pure flammable liquids is vapour inhalation causing narcosis, oxygen displacement in enclosed spaces, and chemical burns on skin contact for liquids with low pH or volatility. Methanol (UN 1230) is the most significant exception: its MFAG reference is Table 2 (toxic substances) because ingestion of small quantities (as little as 10 mL) can cause permanent blindness, and inhalation of high vapour concentrations produces systemic poisoning.

Dangerous goods documentation

Dangerous Goods Declaration

The dangerous goods declaration (DGD) for Class 3 cargo in packaged form must comply with IMDG Code Chapter 5.4 and is completed by the shipper or their agent before the cargo is delivered to the vessel. The mandatory fields for Class 3 are:

• UN number and proper shipping name (in the order specified in IMDG Code 5.4.1.4.1). Example: “UN 1203 GASOLINE.”
• Primary class (3) and subsidiary class if applicable (e.g., “3, 6.1” for methanol).
• Packing group in Roman numerals (I, II, or III).
• Flash point in degrees C (mandatory for Class 3 specifically under IMDG Code 5.4.1.1.6(b)); the value must be taken from a recognized test standard or from the safety data sheet (SDS).
• Total quantity and number of packages.
• Marine pollutant designation if applicable.
• Emergency contact: a 24-hour telephone number for a person or body capable of providing specific technical advice about the cargo.
• Shipper’s declaration of truth: “I hereby declare that the contents of this consignment are fully and accurately described above by the proper shipping name, and are classified, packaged, marked and labelled/placarded, and are in all respects in proper condition for transport by sea according to the applicable international and national governmental regulations.”

The flash-point entry on the DGD is a diagnostic aid for emergency responders. A ship’s officer who finds a DGD with flash point minus 40 degrees C for a drum marked UN 1203 can verify that the PG II assignment and the stowage category B are consistent. A flash point of minus 45 degrees C for a drum labeled as a PG III substance would be a discrepancy requiring immediate investigation with the shipper before acceptance.

Container Packing Certificate

When Class 3 cargo is packed into a freight container by the shipper or a packing agent, a Container Packing Certificate (CPC) must accompany the DGD. The CPC confirms that:

1. The container was clean and free of residue before packing.
2. Packages that are not leaking were selected.
3. Marking and labelling of individual packages are correct.
4. The container has been properly placarded with Class 3 diamonds on all four sides plus the UN number plates.
5. The cargo stowage inside the container is consistent with the compatibility requirements (no incompatible substances in the same container unless IMDG Code segregation table permits).
6. Blocking and bracing prevents package movement under transport conditions.

The CPC is a legal document under IMDG Code 5.4.2. A shipmaster is entitled to refuse a container for which the CPC is absent or materially incomplete.

Marking and labelling

The IMDG Code Chapter 5.2 specifies the label requirements. Class 3 packages must carry:

• The Class 3 label: a diamond with a flame symbol, red background, and the numeral “3” in the bottom corner. Dimensions are at least 100 mm × 100 mm for packages and 250 mm × 250 mm for IBCs; full-size 250 mm × 250 mm diamonds (placards) on freight containers.
• The UN number on the package in 12 mm high digits, preceded by “UN,” adjacent to the proper shipping name.
• If a subsidiary hazard applies, the subsidiary hazard label in addition to the primary Class 3 label.
• If the substance is a marine pollutant, the marine-pollutant mark (fish-and-tree symbol) in addition to all other required labels.

The sibling article IMDG marking, labelling, and placarding covers the full labelling regime across all classes.

Class 3 in practice: selected UN entries in detail

UN 1203 Gasoline (Petrol, Motor Spirit, Petroleum Spirit)

Gasoline is the single highest-volume Class 3 packaged cargo by number of individual shipments worldwide. It is a complex mixture of approximately 200 hydrocarbons, predominantly C4 to C12 paraffins, isoparaffins, cycloalkanes, and aromatics. Summer-grade and winter-grade gasoline have different distillation profiles; the IBP of typical gasoline ranges from 30 to 40 degrees C depending on the region and season. Flash point is typically minus 40 degrees C, giving PG II.

Small-quantity gasoline shipments occur as:

• Fuel in portable generators and power equipment (limited quantities apply when net quantity per package does not exceed 5 litres under IMDG Code 3.4).
• Racing fuel and aviation gasoline (AVGAS, UN 1203 or UN 1257).
• Gasoline in containers for remote-site delivery where pipelines or tanker calls are not economic.

UN 1203 in full PG II packages must be stowed category B. The flash-point declaration on the DGD must be a measured value; the default of “minus 40 degrees C” from published SDS data is acceptable only if the actual batch has not been tested and the SDS value is not a maximum.

UN 1170 Ethanol and ethanol solutions

Ethanol (ethyl alcohol) shipped in concentrations above 24% alcohol by volume is Class 3. Below 24% alcohol by volume, the solution is not Class 3 (the flash point of 24% ethanol/water solution is above 60 degrees C, outside the Class 3 boundary). The exact boundary depends on the mixture composition; the IMDG Code sets the 24% volume threshold as the presumptive classification rule for beverage-type ethanol solutions in the absence of test data.

Fuel ethanol (E100, anhydrous ethanol for blending with gasoline) is UN 1170, Class 3, PG II, flash point 13 degrees C. Denatured industrial alcohol follows the same classification unless the denaturant changes the flash point.

Ethanol’s relatively high IBP (78 degrees C) gives PG II rather than PG I, but its flash point of 13 degrees C makes it significantly more hazardous on a warm-deck spill than its packing group label might suggest. Ethanol fires are nearly invisible in daylight (the flame is pale blue), which creates a particular risk for crew who may walk into a burning ethanol spill without seeing the flame.

UN 1230 Methanol

Methanol (methyl alcohol, wood alcohol) is Class 3 PG II with subsidiary Class 6.1. The toxic hazard dominates the medical-response protocol: the lethal oral dose for an adult human is approximately 1 mL/kg body weight (roughly 70 mL for a 70 kg person). Inhalation of vapour at 200 ppm over several hours produces systemic toxicity without immediate sensory warning (methanol’s odour threshold of 100 to 200 ppm overlaps with the toxicity threshold, providing almost no safety margin by smell alone).

Methanol is also a component of fuel-blending operations and is shipped in large quantities to LPG terminals and chemical plants in IBCs and tank containers. The cargo ethanol segregation calculator also covers methanol and similar Class 3 + toxic cargo in the IBC Code context: see the cargo ethanol segregation calculator.

UN 1131 Carbon Disulfide

Carbon disulfide is among the most hazardous Class 3 substances encountered in packaged marine transport. Its auto-ignition temperature of 90 degrees C means it can ignite on a steam radiator, an incandescent light fitting, or any warm surface without an open flame. Its flash point of minus 30 degrees C and vapour density of 2.64 (air = 1) ensure that any spill produces a heavy vapour layer at deck level that travels downhill toward ignition sources. It also has a subsidiary Class 6.1 toxic designation. UN 1131 is stowage category E (on deck only) precisely because the vapour, if released under deck, would accumulate and reach auto-ignition temperature on ordinary ship’s electrical equipment.

Limitations

The information in this article reflects the IMDG Code 2022 Edition, Amendment 41-22, which became mandatory on 1 January 2024. The IMDG Code is amended on a two-year cycle by the IMO’s sub-committee on Carriage of Cargoes and Containers (CCC); Amendment 42-24 is currently in preparation and will enter force in 2026. Shippers, carriers, and freight forwarders should always verify classification against the current consolidated DGL, not against historical classifications or summary tables.

Flash point values cited in this article for specific substances are literature values drawn from the IMDG DGL and the UN Model Regulations. Actual batch flash points for petroleum products and solvent blends may differ from literature values by several degrees C depending on composition. The flash point declared on the DGD must be based on actual testing per a recognized standard or on the manufacturer’s SDS for the specific batch.

The packing group assignment rules described here apply to pure Class 3 substances and to simple blends where test data is available. For complex mixtures, reactive systems, or substances with multiple competing hazard criteria, classification must be performed by a competent authority-qualified dangerous goods classifier. This article does not substitute for that expert assessment.

Stowage category and segregation assignments are taken from the standard DGL entries. Ships with special cargo configurations, Ro-Ro vessels, container ships with restricted holds, or vessels carrying Class 3 in combination with unusual co-cargoes should seek a port-state-accepted dangerous goods stowage plan verified by a Class I DG officer or a recognized dangerous goods specialist.

The MFAG first-aid references in this article are indicative. Ship masters should carry the current printed MFAG aboard and consult it, alongside the IMO MSC.1/Circ.1428 (Rev.1) list of approved coast-guard medical consultation centres, for any actual medical emergency involving Class 3 substances.

See also

• IMDG Class 1: Explosives
• IMDG Class 2: Gases
• IMDG Class 4: Flammable Solids
• IMDG Class 5: Oxidisers and Organic Peroxides
• IMDG Class 6: Toxic and Infectious Substances
• IMDG Class 8: Corrosive 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
• MARPOL Annex I
• MARPOL Annex II: Noxious Liquid Substances
• IBC Code
• IMSBC Code
• Chemical Tanker
• IMDG segregation calculator
• IMDG packing group calculator
• IMDG packing group from flash point calculator
• IMDG EmS lookup calculator
• IMDG limited quantity calculator
• Container IMDG class lookup
• IMDG tank container calculator
• Flash point compliance check calculator
• ASTM D93 flash point calculator
• ASTM D7094 flash point calculator
• Cargo ethanol segregation calculator
• Tanker cargo cooling chemical calculator
• IMO IMDG general calculator