IMDG Code — dangerous goods classes

The International Maritime Dangerous Goods (IMDG) Code is the IMO instrument that implements SOLAS Chapter VII for packaged dangerous cargo and MARPOL Annex III for marine pollutants. It is mandatory for all ships covered by SOLAS carrying dangerous goods in packaged form. The code is republished biennially (current edition 41-22, in force 1 January 2024 and mandatory from 1 January 2025) and contains the Dangerous Goods List, packing instructions, transport documents, and the Stowage and Segregation rules.

Goods are identified by a four-digit UN number, a Proper Shipping Name, a class (and division), a packing group, and any subsidiary risks. Packages are marked and labelled with diamond labels matching the class; freight containers are placarded on all four sides plus a UN number panel.

Classes

• 1Explosives

  Substances and articles capable of mass explosion, projection, or fire.

  • 1.1 — Mass explosion hazard. TNT, dynamite, military munitions.
  • 1.2 — Projection hazard. Detonators with fragments.
  • 1.3 — Fire hazard, minor blast / projection. Smokeless powder, propellants.
  • 1.4 — No significant hazard, ignition or initiation effects confined to the package. Sporting ammunition, signal cartridges.
  • 1.5 — Very insensitive substances with a mass-explosion hazard. Blasting agents, ANFO.
  • 1.6 — Extremely insensitive articles with no mass-explosion hazard. Insensitive munitions.

  Notes: Compatibility groups A through S add a letter to the division (e.g. 1.1D).

• 2Gases

  Compressed, liquefied, dissolved, refrigerated liquefied, or sorbed gases.

  • 2.1 — Flammable gases. LPG, propane, butane, acetylene, hydrogen.
  • 2.2 — Non-flammable, non-toxic gases. Nitrogen, CO₂, refrigerants, compressed air.
  • 2.3 — Toxic gases. Chlorine, ammonia, hydrogen sulphide, fumigants.

  Notes: Cylinders must be secured upright with valve protection. Acetylene is forbidden in hold stowage.

• 3Flammable liquids

  Liquids with closed-cup flash point ≤ 60 °C (or ≤ 100 °C for some heated transport).

  Examples: Petrol/gasoline (PG II); Diesel oil (PG III); Methanol, ethanol, acetone; Paints, adhesives, solvent thinners

• 4Flammable solids

  Solids that are readily combustible or that may cause fire through friction, self-heating, or contact with water.

  • 4.1 — Flammable solids. Matches, sulphur, naphthalene, nitrocellulose.
  • 4.2 — Substances liable to spontaneous combustion. White phosphorus, cotton waste oily, fishmeal, copra.
  • 4.3 — Substances which on contact with water emit flammable gases. Calcium carbide, sodium, lithium, magnesium powder.
• 5Oxidising substances and organic peroxides

  Substances which release oxygen, supporting combustion of other materials.

  • 5.1 — Oxidising substances. Ammonium nitrate, hydrogen peroxide, sodium chlorate, calcium hypochlorite.
  • 5.2 — Organic peroxides (Type A–G). MEKP, BPO, dicumyl peroxide. Most require temperature control.

  Notes: Calcium hypochlorite (pool chlorine) implicated in multiple container ship fires; stowage rules tightened in 2018 amendments.

• 6Toxic and infectious substances

  Substances liable to cause death or serious injury to human health if swallowed, inhaled, or by skin contact.

  • 6.1 — Toxic substances. Cyanides, pesticides, mercury compounds, arsenic, phenol.
  • 6.2 — Infectious substances (Category A & B). Cultures, clinical specimens, biological products. UN 2814 / 2900 / 3373.
• 7Radioactive material

  Activity concentration > 10× exempt values; categorised by transport index and surface dose rate.

  Examples: UN 2910–3334 (LSA, SCO, Type A, Type B, fissile, UF6); Carriage subject to flag and IAEA Transport Regulations; Categories I-WHITE, II-YELLOW, III-YELLOW labels

• 8Corrosive substances

  Substances which cause severe damage to skin or to other freight by chemical action.

  Examples: Sulphuric acid, hydrochloric acid, nitric acid; Sodium hydroxide, potassium hydroxide; Mercury (UN 2809); Lithium-ion battery electrolyte

• 9Miscellaneous dangerous substances and articles

  Hazards not covered by classes 1–8, including marine pollutants and elevated-temperature substances.

  Examples: UN 3480 / 3481 lithium-ion batteries; UN 3090 / 3091 lithium-metal batteries; UN 3077 / 3082 environmentally hazardous substances (marine pollutants); UN 3257 elevated-temperature liquids; Dry ice (UN 1845); Genetically modified organisms (UN 3245)

Packing groups

• PG I — Great danger. Substances of high hazard.
• PG II — Medium danger. Substances of moderate hazard.
• PG III — Minor danger. Substances of low hazard.

Classes 1, 2, 5.2, 6.2, and 7 are not assigned packing groups.

Segregation table

Cell value in the IMDG Segregation Table indicates the segregation requirement between two classes:

• 1 — Away from — separated within the same hold/compartment by 3 m horizontally.
• 2 — Separated from — different holds, or one vertical compartment apart on deck.
• 3 — Separated by a complete compartment or hold from — minimum 6 m horizontally if on deck.
• 4 — Separated longitudinally by an intervening complete compartment or hold from — minimum 24 m on deck.
• X — No general segregation, see DG List for individual entry.

Documents required

• · Dangerous Goods Declaration (DG Note) — UN number, PSN, class, PG, marine pollutant, flash point, EmS code, total quantity, packaging.
• · Container / Vehicle Packing Certificate — signed by the person responsible for stowage.
• · Manifest / Stowage Plan — onboard, listing each consignment's position.
• · Emergency Response (EmS) and Medical First Aid (MFAG) — codes referenced from the DG List, on the bridge.

See also

• · MARPOL annexes — Annex III is the source of the marine pollutant regime.
• · Ship types — chemical, gas, and container vessels carry these cargoes.
• · Distress procedures — for cargo fires and toxic releases.

This is a quick-reference summary. The authoritative text is the IMO publication IMDG Code (current biennial edition) including all amendments.