IMDG Code Classification: Complete Guide to Dangerous Goods Classes

Shipping dangerous goods (DG) by sea requires strict compliance with the International Maritime Dangerous Goods (IMDG) Code, a comprehensive set of regulations developed by the International Maritime Organization (IMO). The IMDG Code classifies hazardous materials into 9 hazard classes, each with specific packaging, labeling, documentation, and stowage requirements. Misclassification of dangerous goods can result in container fires, chemical spills, vessel explosions, severe injuries, and multi-million dollar liabilities.

For exporters shipping dangerous goods from Global - whether chemicals, lithium batteries, paints, or fireworks - understanding the IMDG classification system is essential. This comprehensive guide details all 9 hazard classes with examples, explains packaging group requirements, covers labeling and placarding rules, and outlines the documentation needed for compliant DG shipments by sea.

Overview of the IMDG Code

The IMDG Code is the international standard for the safe transportation of dangerous goods by sea. First published in 1965, it is updated every two years (in even-numbered years). The current edition, IMDG Code Amendment 42-26, became mandatory on January 1, 2026. The code covers classification, packaging, marking, labeling, placarding, documentation, stowage, segregation, and emergency response for dangerous goods shipped by sea.

The IMDG Code divides dangerous goods into 9 hazard classes based on the specific type of hazard they present. Some classes are further divided into divisions. Each dangerous good is also assigned a UN number (a four-digit identifier) and a packing group (I, II, or III) indicating the degree of danger:

• Packing Group I: Great danger - high hazard substances
• Packing Group II: Medium danger - medium hazard substances
• Packing Group III: Minor danger - low hazard substances

Not all dangerous goods are assigned a packing group - some classes (like Class 1 explosives and Class 7 radioactive materials) use their own classification systems. The packing group determines the required packaging performance level: PG I requires the most robust packaging, PG III the least.

Class 1: Explosives

Class 1 covers substances and articles that have a mass explosion hazard, a projection hazard, or a fire hazard. This class is divided into six divisions based on the type of hazard:

• Division 1.1: Substances and articles with a mass explosion hazard (e.g., TNT, dynamite)
• Division 1.2: Substances with a projection hazard but no mass explosion hazard (e.g., certain rockets, flares)
• Division 1.3: Substances with a fire hazard and minor blast/projection hazard (e.g., fireworks, some rocket propellants)
• Division 1.4: Substances presenting no significant hazard (e.g., safety fuses, some ammunition)
• Division 1.5: Very insensitive substances with mass explosion hazard (e.g., blasting agents)
• Division 1.6: Extremely insensitive articles with no mass explosion hazard

Common examples: Fireworks (UN0336), ammunition (UN0012), flares (UN0191), detonators (UN0029). China is one of the world's largest exporters of fireworks, particularly from Hunan and Jiangxi provinces.

Shipping requirements: Class 1 explosives require special stowage (usually "on deck only"), segregation from other dangerous goods, and in some cases, government transport permits. Many ports restrict the handling and storage of Class 1 explosives.

Class 2: Gases

Class 2 covers gases compressed, liquefied, or dissolved under pressure. The class is divided into three divisions based on the primary hazard:

• Division 2.1: Flammable gases (e.g., propane UN1978, butane UN1011, hydrogen UN1049)
• Division 2.2: Non-flammable, non-toxic gases (e.g., nitrogen UN1066, carbon dioxide UN2187, argon UN1006)
• Division 2.3: Toxic gases (e.g., chlorine UN1017, ammonia UN1005, methyl chloride UN1063)

Common examples: LPG in cylinders, refrigerant gases, welding gases, aerosol products. Gases are typically shipped in steel cylinders, tubes, or ISO tanks.

Shipping requirements: Cylinders must be properly filled, closed, and fitted with valve protection. Pressure receptacles require periodic inspection and testing. Flammable and toxic gases require specific stowage and segregation.

Class 3: Flammable Liquids

Class 3 covers liquids with a flash point not exceeding 60°C (closed cup). This is one of the most commonly shipped DG classes, including a vast range of industrial chemicals, fuels, solvents, and consumer products.

• Common examples: Gasoline (UN1203), diesel fuel (UN1202), acetone (UN1090), methanol (UN1230), ethanol (UN1170), paint (UN1263), perfume products (UN1266), adhesives (UN1133)
• Packing groups: PG I (flash point < 23°C, initial boiling point < 35°C), PG II (flash point < 23°C, boiling point > 35°C), PG III (flash point 23-60°C)

Shipping requirements: Class 3 liquids are shipped in steel or plastic drums, IBC totes, or ISO tanks depending on volume. Packaging must be compatible with the liquid (some solvents degrade certain plastics). Vents may be required for liquids that expand with temperature changes.

Class 4: Flammable Solids

Class 4 covers substances that are easily combustible, may cause fires through friction, or emit flammable gases when in contact with water. Three divisions:

• Division 4.1: Flammable solids, self-reactive substances, and desensitized explosives (e.g., camphor UN2717, matches UN1945, naphthalene UN1334)
• Division 4.2: Substances liable to spontaneous combustion (e.g., white phosphorus UN1381, activated carbon UN1362, fish meal UN1374)
• Division 4.3: Substances emitting flammable gases when wet (e.g., calcium carbide UN1402, sodium UN1428, magnesium UN1869)

Shipping requirements: Class 4 substances require careful packaging to prevent ignition sources. Self-reactive substances may require temperature control. Water-reactive substances (4.3) must be kept completely dry and segregated from all water sources.

Class 5: Oxidizing Substances and Organic Peroxides

• Division 5.1: Oxidizing substances - substances that cause or contribute to combustion by yielding oxygen (e.g., ammonium nitrate UN1942, hydrogen peroxide UN2014, potassium permanganate UN1490)
• Division 5.2: Organic peroxides - thermally unstable substances that may undergo exothermic self-accelerating decomposition (e.g., methyl ethyl ketone peroxide UN3105, dibenzoyl peroxide UN3104)

Shipping requirements: Oxidizers must be segregated from flammable materials. Organic peroxides may require temperature-controlled storage and transport. Some organic peroxides are forbidden for sea transport or require special permits.

Class 6: Toxic and Infectious Substances

• Division 6.1: Toxic substances - substances that can cause death or serious injury if swallowed, inhaled, or absorbed through skin (e.g., phenol UN1671, nicotine UN1654, aniline UN1547, pesticides various UN numbers)
• Division 6.2: Infectious substances - substances known or reasonably expected to contain pathogens (e.g., Category A infectious substances UN2814/UN2900, Category B UN3373, medical waste UN3291)

Shipping requirements: Toxic substances require packaging that prevents any leakage. Infectious substances must be triple-packaged according to WHO/UN packaging instructions. Category A infectious substances require special transport permits and may be restricted on certain routes.

Class 7: Radioactive Material

Class 7 covers any material with a specific activity greater than 70 Bq/g. This includes medical isotopes, industrial radiography sources, nuclear fuel, and certain consumer products containing radioactive components.

• Common examples: Cobalt-60 (UN2915), Iridium-192 (UN2915), depleted uranium (UN2909), uranium hexafluoride (UN2977)

Shipping requirements: Radioactive materials are among the most heavily regulated dangerous goods. Packaging must meet specific performance standards based on the activity and form of the material. Transport requires a shipper's declaration, transport index (TI) calculation, and specific stowage and segregation. Many ports and carriers have additional restrictions on Class 7.

Class 8: Corrosive Substances

Class 8 covers substances that cause visible destruction or irreversible alteration of living tissue at the site of contact, or that cause severe corrosion to steel or aluminum. This is another commonly shipped DG class from Global.

• Common examples: Sulfuric acid (UN1830), hydrochloric acid (UN1789), nitric acid (UN2031), sodium hydroxide (UN1824), battery fluid (UN2796), acetic acid (UN2790)
• Packing groups: PG I (severe corrosion to skin within 60 min), PG II (corrosion within 3 days), PG III (corrosion within 14 days)

Shipping requirements: Corrosive substances require packaging resistant to the specific chemical. Steel drums are suitable for some acids but not for hydrochloric acid (which requires plastic-lined or all-plastic packaging). Corrosives must be segregated from Class 4 and other incompatible substances.

Class 9: Miscellaneous Dangerous Goods

Class 9 covers substances and articles that present a danger not covered by other classes. This is a diverse and growing category, particularly important for modern trade.

• Lithium batteries: UN3480 (lithium-ion batteries), UN3481 (lithium-ion in equipment or packed with), UN3090 (lithium metal batteries), UN3091 (lithium metal in equipment or packed with)
• Environmentally hazardous substances: UN3082 (environmentally hazardous liquid), UN3077 (environmentally hazardous solid)
• Other examples: Dry ice (UN1845), magnets (UN2807), asbestos (UN2212/UN2590), lithium battery-powered vehicles (UN3171)

Shipping requirements: Class 9 requirements vary significantly by substance. Lithium batteries require specialized packaging (UN-spec boxes), marking (lithium battery label, Class 9 label), and may be subject to state-of-charge limits (30% for air freight). Environmentally hazardous substances require the "dead fish and dead tree" mark.

DG Packaging Requirements

Dangerous goods packaging must meet UN performance standards. The packaging type is designated by a UN packaging code:

• 1A1/1A2: Steel drums (non-removable/removable head)
• 1H1/1H2: Plastic drums
• 4G: Fiberboard boxes (for inner packaging)
• 4H1: Expanded plastic boxes
• IBCs: Intermediate Bulk Containers (31HA1 = plastic composite IBC)

UN packaging codes include the packing group for which the packaging is tested (X=PG I, Y=PG II, Z=PG III). A packaging tested for PG I can be used for PG II and III, but not vice versa.

DG Labeling and Placarding

Each package of dangerous goods must display:

• Class label: Diamond-shaped hazard label (100mm x 100mm for packages, 250mm x 250mm for containers) showing the class symbol and class number
• UN number: Prefixed with "UN" (e.g., UN1263 for paint)
• Proper shipping name: The official IMDG Code name for the substance
• Packing group: Where applicable (PG I, II, or III)
• Orientation arrows: For liquid packages (up arrows indicating "this way up")

Containers carrying dangerous goods must display placards (250mm x 250mm diamond labels) on all four sides, showing the hazard class. For certain goods, the UN number must also be displayed on the placard.

DG Documentation Requirements

Dangerous goods shipments require specific documentation:

• Dangerous Goods Declaration (DGD): The primary DG document, signed by the shipper, certifying that the cargo complies with IMDG Code requirements. Includes UN number, proper shipping name, class, packing group, number and type of packages, total quantity, and emergency contact information.
• Container/Vehicle Packing Certificate: Certifies that the container was packed in accordance with IMDG Code requirements, including proper distribution of weight, segregation of incompatible goods, and securing of cargo.
• MSDS (Material Safety Data Sheet): Provides detailed information about the substance's properties, hazards, and emergency response procedures. While not always required by the IMDG Code, carriers and ports typically require it.
• Emergency Response Procedures: Information on how to respond to incidents involving the specific dangerous goods, including fire fighting, spill response, and first aid measures.

Key Takeaways for IMDG DG Shipping

• The IMDG Code classifies dangerous goods into 9 hazard classes, each with specific packaging, labeling, and stowage requirements
• Each DG shipment requires a UN number, proper shipping name, hazard class, and packing group (where applicable)
• Packaging must meet UN performance standards - always use packaging rated for your packing group or higher
• Lithium batteries (Class 9) are the fastest-growing DG category and require specialized packaging and UN38.3 compliance
• DG containers must display placards on all four sides, and packages must have class labels and UN numbers
• The Dangerous Goods Declaration is the key compliance document - never sign a DGD without verifying all information
• Incompatible dangerous goods must be segregated according to IMDG Code segregation tables
• Work with a DG-certified freight forwarder to ensure full compliance and avoid refusals, fines, or accidents

Conclusion

Proper classification and compliance with the IMDG Code are essential for safe and legal dangerous goods shipping by sea. With 9 hazard classes, hundreds of UN numbers, and constantly evolving regulations, DG shipping requires specialized knowledge and careful attention to detail. Misclassification or non-compliance can result in refused shipments, port fines, cargo fires, and even vessel emergencies.

SHAQ Logistics is a dangerous goods specialist with extensive experience shipping all 9 IMDG classes from Global. Our DG-certified team handles classification verification, packaging consultation, documentation preparation, carrier booking, and port coordination for chemicals, batteries, gases, and all other hazardous materials. Contact us for expert DG shipping services and compliance support.