Dangerous Goods by Sea: IMDG Classes, Packing & Documentation Guide

Dangerous goods are the most heavily regulated cargo that moves across the ocean. A single mis-declared carton of lithium batteries or an incorrectly packed drum of flammable liquid can delay an entire vessel, trigger fines from the carrier and the port, and void your insurance if something goes wrong. This guide explains how the IMDG Code classifies hazardous cargo, what the packing and marking rules demand, and the documentation chain that Indian exporters and importers must follow — the same checklist our certified DG team uses before accepting any hazardous booking.

What the IMDG Code actually is

The International Maritime Dangerous Goods (IMDG) Code is the mandatory rulebook under the SOLAS convention for moving hazardous cargo by sea. It is updated every two years and administered by the International Maritime Organization (historically known as IMCO — the Inter-Governmental Maritime Consultative Organization, which is why the industry still says 'IMCO class' when it means the IMDG hazard class). Air shipments follow a parallel but stricter set of rules: the IATA Dangerous Goods Regulations.

'IMCO class' and 'IMDG class' mean the same thing. IMCO was renamed IMO in 1982, but the older abbreviation survives on labels, rate sheets and booking forms worldwide.

The nine IMDG hazard classes

UN numbers and Proper Shipping Names

Every dangerous good is identified by a four-digit UN number and a Proper Shipping Name (PSN) — for example UN 1263, 'Paint', or UN 3481, 'Lithium ion batteries contained in equipment'. The UN number drives everything else: the permitted packaging, the segregation rules on the vessel, and the emergency response codes. Never book DG cargo using trade names like 'cleaning solution'; the booking must carry the exact PSN from the IMDG Dangerous Goods List.

Packing Groups I, II and III

Within most classes, cargo is further graded into packing groups that reflect the degree of danger. Packing Group I is high danger (concentrated acids, very flammable solvents), PG II is medium danger, and PG III is low danger (dilute paints, mild corrosives). The packing group determines which packaging performance level — X, Y or Z — is permitted: PG I requires X-rated packaging, PG II allows X or Y, and PG III allows X, Y or Z.

Packing, marking and labelling requirements

• UN-approved packaging: drums, jerricans, boxes and IBCs must carry a valid UN packaging mark matching the packing group of the contents.
• Hazard labels: every package bears the class diamond label (plus subsidiary risk labels where applicable), minimum 100 mm × 100 mm for packages.
• Marking: each package shows the UN number and Proper Shipping Name, orientation arrows for liquids, and the marine pollutant mark where applicable.
• Segregation: incompatible classes (e.g., oxidizers away from flammables, acids away from cyanides) must be separated per the IMDG segregation table — your forwarder plans the stowage with the carrier.
• Container packing certificate: the person who stuffs the container certifies it was packed, segregated, secured and placarded correctly.
• Container placards: enlarged 250 mm class placards on all four sides of the container, plus UN numbers where required.
• 24-hour emergency contact and, for many shipments, an Emergency Response Guide or TREM card carried with the documents.

Documents needed for DG shipments from India

1. 1Material Safety Data Sheet (SDS/MSDS) — the 16-section safety data sheet from the manufacturer, used to classify the cargo.
2. 2Dangerous Goods Declaration (DGD / Multimodal DG Form) — signed by a trained and certified person, declaring the UN number, PSN, class, packing group and quantity.
3. 3Container Packing Certificate — usually combined with the DGD, certifying safe stuffing and segregation.
4. 4UN packaging test certificates for the drums, boxes or IBCs used.
5. 5Booking with DG details submitted to the shipping line well before cut-off — most lines require DG approval 48–72 hours before vessel loading.
6. 6For air freight: the IATA Shipper's Declaration for Dangerous Goods instead of the sea DGD, prepared by IATA DG-certified staff.
7. 7Regulatory permits where applicable — e.g., PESO approvals for certain gases and explosives, or export licences for controlled chemicals.

Mis-declaring DG cargo as general cargo is a criminal offence in most jurisdictions, and carriers now levy mis-declaration penalties of USD 10,000–30,000 per container. When in doubt, send us the SDS before booking — classification takes minutes; a vessel fire does not.

Frequently asked questions

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