The International Maritime Dangerous Goods (IMDG) Code is a mandatory instrument under the International Convention for the Safety of Life at Sea (SOLAS Chapter VII) for the transport of dangerous goods by sea, giving effect to the recommendations of the United Nations Committee of Experts on the Transport of Dangerous Goods. Its purposes are:

• To protect the ship, crew, passengers and the marine environment by ensuring dangerous goods are carried in a safe manner consistent with their hazards.
• To provide a uniform, internationally agreed code of practice so that cargo is classified, packed, labelled, documented, stowed and segregated consistently worldwide.
• To prevent accidents, explosions, fires, toxic releases and adverse reaction between incompatible goods, and to guide emergency response and casualty handling.
• To instruct shore and shipboard personnel in correct handling, stowage and segregation of dangerous cargo.

Structure and classification:

• The Code classifies dangerous goods into nine classes:
• Class 1: Explosives.
• Class 2: Gases (flammable, non-flammable/non-toxic, toxic).
• Class 3: Flammable liquids.
• Class 4: Flammable solids, substances liable to spontaneous combustion, substances which emit flammable gases in contact with water.
• Class 5: Oxidising substances and organic peroxides.
• Class 6: Toxic and infectious substances.
• Class 7: Radioactive material.
• Class 8: Corrosives.
• Class 9: Miscellaneous dangerous substances and articles (including environmentally hazardous substances, marine pollutants, elevated-temperature substances).
• Each substance is given a UN number, proper shipping name, and is assigned a packing group (I, II or III) according to degree of danger (great danger, medium, minor).
• Each entry has a Dangerous Goods List giving properties, packing instructions, segregation group, stowage, emergency schedule and marine pollutant status.
• The Code gives segregation and stowage requirements (compatibility, separation distances), based on "segregation" terms (away from, separated from, separated by a complete compartment, or separated by an intervening complete compartment), and stowage by "on deck/in accordance with the Code".
• It covers packaging (with performance tests), marking and labelling (hazard labels and marine pollutant mark), placarding, and documentation (Dangerous Goods Manifest, container packing certificates), and the emergency response information (EMS) needed on board.

Packaging: Dangerous goods must be packed in packagings that are of good quality, properly closed, capable of withstanding the stresses of transport (including humid, corrosive and varying temperature conditions) and manufactured and tested to the UN performance standards. Packaging must be compatible with the hazardous properties of the substance and, where relevant, be provided with inner packagings, cushioning and absorbents. Damaged or leaking packagings must be rejected.

Labelling: Each package must bear the proper shipping name and the correct hazard class label (diamond-shaped label) indicating the primary hazard; additional labels for subsidiary hazards (e.g. marine pollutant) and the UN number. Containers must display placards and MARPOL marine-pollutant marks. Marking must be durable and legible.

Documentation: A Dangerous Goods Transport Document/Manifest giving the proper shipping name, UN number, class, packing group, quantity, and the emergency contact; the container/vehicle packing certificate (signed by the packer); and the shipside Dangerous Goods List or Manifest, which is required to be carried and displayed on the ship, plus stowage plan. The Master must be given the required information and the ship's Fire Control Plan/SOPEP amended as necessary; the Master or designated officer signs the declaration of compliance on the manifest.

Responsibilities:

• The shipowner/operator and cargo handling facility must ensure their personnel are properly trained and familiar with the IMDG Code, that goods are accepted only with correct documentation and labels, and are stowed and segregated on board in accordance with the plan.
• The Master is responsible for ensuring the ship carries a current copy of the Code, a proper stowage plan, and that dangerous goods are loaded, stowed, segregated, secured and reported correctly; the Master must be informed of the nature of the cargo and its hazards.
• Crewmembers must follow the operational procedures: correct handling, lashing, securing, ventilation, monitoring (e.g. of temperature or flammable gas), use of the EMS (Emergency Schedules), and must report damage/deficiency; they must wear required personal protective equipment and follow the stowage and segregation rules.
• On tankers and gas carriers the coded cargo-specific requirements apply (MARVS, temperature, etc.). Correct compliance is verified by port State control and carriage restrictions are enforced under SOLAS VII and the Code.