Shipping Dangerous Goods by Sea: Why Booking as General Cargo Gets Refused, and How IMDG Classes, UN Numbers, and Lithium Batteries Work

A shipper sends power banks and gets the booking refused at the last minute. A cosmetics company loads perfume and nail remover as ordinary cargo and the shipment is stopped at the port. The common thread is not knowing these are dangerous goods. Dangerous goods are booked, documented, and packed in a completely different way from general cargo, and above all, tendering them as ordinary cargo without realizing gets the shipment refused or sent back.

First, decide whether your cargo is dangerous

You do not judge this by feel. Ocean transport is governed by the International Maritime Dangerous Goods (IMDG) Code, set by the International Maritime Organization (IMO), which sorts dangerous goods into nine classes by hazard.

The table alone shows how everyday consumer goods qualify: perfume (Class 3), aerosols (Class 2), bleach (Class 5), power banks (Class 9). Whether your goods are dangerous, and which class, is confirmed on the safety data sheet (SDS or MSDS). Of its 16 sections, section 14, transport information, lists the cargo's class, UN number, and packing group.

The UN number is a four-digit code assigned to each dangerous good that, with its proper shipping name (PSN), identifies exactly what the cargo is worldwide. The packing group (PG) grades the degree of danger as I, II, or III, with I the most dangerous and III the least. These three, the class, UN number, and packing group, are where every dangerous-goods procedure begins.

Lithium batteries: the most common trap

Of all dangerous goods, lithium batteries cause the most trouble in practice. Power banks, laptops, power tools, and wireless earbuds all contain them, yet shippers often fail to recognize them as dangerous. Lithium batteries are Class 9, and the UN number splits by how they ship.

• UN3480 is for batteries shipped on their own, such as power banks or battery packs by themselves.
• UN3481 is for batteries contained in equipment or packed with equipment, such as a finished product with the battery installed.

The document you cannot skip is the UN38.3 test summary, which proves the battery passed safety tests for vibration, shock, temperature, and pressure. Under an IMDG Code amendment it has been mandatory before transport since 2020, so get it from the battery maker or supplier at the order stage; without it the shipment does not move.

Dangerous goods need carrier approval before you book

General cargo books if space exists; dangerous goods work the other way around. Before you place the booking, the carrier must approve whether that dangerous good can go on that vessel.

The sequence usually runs like this. You submit the class, UN number, and packing group from the SDS to the carrier to confirm the cargo can move from origin to final destination. Some carriers and routes will not accept certain dangerous goods at all, so this pre-check has to pass before a booking stands. Once approved, packing the dangerous goods into the container triggers a statutory inspection, after which a container packing certificate is issued, and the shipper files a dangerous-goods declaration with the carrier. Dangerous-goods shipments also carry their own surcharges, and the structure of those charges is covered in ocean freight surcharges explained.

Packing, marking, and segregation

Dangerous goods do not go in just any box. They must be packed in UN-certified packaging that passed performance tests for the packing group, and the outside is marked with the diamond-shaped class placard and the UN number. That marking lets the port and the ship see at a glance what the cargo is and how to handle it.

Loading several dangerous goods together adds segregation rules. Because some dangerous goods react if they meet, the IMDG Code specifies which class combinations must be kept apart. Oxidizers and flammable liquids, for example, are dangerous together and must be segregated. Miss this and the cargo fails inspection, or in the worst case it leads to an accident at sea.

A pre-shipment checklist for dangerous goods

Before you ship dangerous goods, line these up.

1. Confirm the hazard: use SDS section 14 to establish your cargo's class, UN number, and packing group.
2. Lithium battery papers: if the cargo contains batteries, determine UN3480 versus UN3481 and secure the UN38.3 test summary.
3. Carrier pre-approval: confirm with the carrier that the dangerous goods can move before you book.
4. Packing and marking: use UN-certified packaging, apply the class placard and UN number, and pass the container inspection.
5. Segregation: when loading several dangerous goods together, stow them per the IMDG segregation rules.

Shipping dangerous goods is not general cargo with extra paperwork bolted on; it moves in a different order from the start. Decide whether your cargo is dangerous first, and prepare the carrier approval and documents at the order stage, and the shipment moves without being refused at booking or stopped at the port.

This guide is general information as of July 2026. Dangerous-goods classification and the documentation, packing, and segregation requirements vary by item, IMDG Code amendment, and carrier and route policy, so confirm with the maritime dangerous-goods inspection authority, the carrier, and your forwarder before shipping.