Dangerous goods classes are the nine hazard categories the United Nations uses to sort any substance or article that can harm people, ships or the environment in transport. There are exactly nine: explosives, gases, flammable liquids, flammable solids, oxidizers, toxic and infectious substances, radioactive material, corrosives and miscellaneous dangerous goods.
If you ship anything by sea, from paint to power banks, the class decides how the goods are packed, labelled, declared and stowed on the ship. Get it wrong and the container can be refused at the terminal, stowed in the wrong place, or become the source of a fire in the middle of an ocean. This guide walks through all nine classes, the divisions inside them, the packing groups that rank danger within a class, and how the rules play out on a container ship.
What Dangerous Goods Classes Are and Who Sets Them
The system starts with the UN Recommendations on the Transport of Dangerous Goods, known as the Model Regulations or the "Orange Book". The UN classification rules assign every dangerous substance to a class according to the hazard it presents, or the most predominant hazard when it has several. Some classes are split further into divisions, written as a decimal such as 2.1 or 4.3.
Every mode of transport uses the same nine classes, so a drum of solvent is Class 3 on a truck, a plane and a ship. What changes is the rulebook built on top. Road transport in Europe follows ADR, air cargo follows the ICAO Technical Instructions, and packaged dangerous goods at sea follow the International Maritime Dangerous Goods Code, the IMDG Code.
Each dangerous substance also carries a four-digit UN number and a proper shipping name. When a product has more than one hazard, the most serious one becomes its primary class and the others are listed as subsidiary classes, as Transport Canada explains in its classification scheme.
The 9 Classes of Dangerous Goods at a Glance
Here is how many classes of dangerous goods there are, and what sits in each one.
| Class | Name | Divisions | Typical sea freight examples |
|---|---|---|---|
| 1 | Explosives | 1.1 to 1.6 | Fireworks, ammunition, flares |
| 2 | Gases | 2.1, 2.2, 2.3 | Aerosols, propane, compressed oxygen |
| 3 | Flammable liquids | None | Paint, solvents, perfume, fuel |
| 4 | Flammable solids | 4.1, 4.2, 4.3 | Matches, charcoal, calcium carbide |
| 5 | Oxidizers and organic peroxides | 5.1, 5.2 | Ammonium nitrate, hydrogen peroxide |
| 6 | Toxic and infectious substances | 6.1, 6.2 | Pesticides, medical samples |
| 7 | Radioactive material | None | Medical isotopes, industrial sources |
| 8 | Corrosives | None | Battery acid, caustic soda |
| 9 | Miscellaneous dangerous goods | None | Lithium batteries, dry ice, vehicles |
The class number tells you the type of hazard, not its severity. A Class 9 lithium battery shipment can start a worse fire than a carton of Class 3 nail polish. Severity inside a class is the job of packing groups, covered further down.
Classes 1 to 3: Explosives, Gases and Flammable Liquids
Class 1: Explosives
Class 1 is the only class with six divisions. Division 1.1 covers substances and articles with a mass explosion hazard, 1.2 a projection hazard, and 1.3 a fire hazard with only a minor blast or projection risk. Division 1.4 covers items with no significant hazard, such as many consumer fireworks and small arms cartridges, while 1.5 and 1.6 cover very insensitive substances and articles.
Explosives also carry a compatibility group letter, such as 1.4G or 1.4S, which tells the ship which explosives may be stowed together.
Class 2: Gases
Gases split by what they do when they escape. Division 2.1 is flammable gases such as propane and most aerosols. Division 2.2 is non-flammable, non-toxic gases such as nitrogen, carbon dioxide and compressed air. Division 2.3 is toxic gases such as chlorine and ammonia, the most tightly controlled of the three.
Class 3: Flammable Liquids
Class 3 is the class most importers meet first, because it covers everyday goods: paints, varnishes, adhesives, perfumes, alcohol-based sanitisers and fuels. A liquid falls here when its vapour can ignite at a low temperature, and the flash point helps decide its packing group.
Classes 4 to 6: Flammable Solids, Oxidizers and Toxic Substances
Class 4: Flammable Solids
Class 4 has three divisions with three different fire mechanisms. Division 4.1 covers flammable solids and self-reactive substances, such as matches and some metal powders. Division 4.2 covers substances liable to spontaneous combustion, which can heat up and ignite with no outside spark; charcoal is the classic sea freight example. Division 4.3 covers substances that give off flammable gas in contact with water, such as calcium carbide, which is why they are labelled "dangerous when wet".
Class 5: Oxidizers and Organic Peroxides
Division 5.1 oxidizers do not necessarily burn themselves, but they release oxygen and make other materials burn far more fiercely. Ammonium nitrate fertiliser and pool chlorine products sit here. Division 5.2 organic peroxides, used in resins and plastics manufacturing, are often unstable and some need temperature control throughout the voyage.
Class 6: Toxic and Infectious Substances
Division 6.1 covers substances that can kill or injure if swallowed, inhaled or absorbed through the skin, including many pesticides and industrial chemicals. Division 6.2 covers infectious substances, from diagnostic specimens to cultures, split into Category A and the less dangerous Category B.
Classes 7 to 9: Radioactive, Corrosive and Miscellaneous
Class 7: Radioactive Material
Class 7 covers medical isotopes, industrial gauges and nuclear fuel cycle materials. It has its own labelling system based on radiation level, and it is the one class most general freight forwarders will not accept without a specialist.
Class 8: Corrosives
Corrosives destroy skin or eat through metal. Battery acid, caustic soda, hydrochloric acid and many cleaning concentrates are Class 8. On a ship, the concern is a leaking drum attacking the container floor, neighbouring cargo or the hull structure.
Class 9: Miscellaneous Dangerous Goods and Lithium Batteries
Class 9 collects hazards that do not fit elsewhere, including environmentally hazardous substances, dry ice, asbestos and vehicles. For container shipping, the headline entry is lithium batteries. According to CINS guidelines published in April 2026, lithium ion batteries ship as UN 3480, and lithium ion batteries contained in or packed with equipment ship as UN 3481, both Class 9.
Smaller batteries can travel under Special Provision 188, which exempts them from full dangerous goods declaration if they stay within watt-hour limits and are packed to prevent short circuits. Cells that fail the UN 38.3 test do not qualify. The exemption is narrow, and treating every battery shipment as exempt is one of the main routes to a misdeclared container.
Packing Groups: How Danger Is Ranked Within a Class
Most classes rank their substances into three packing groups. Packing Group I means high danger, Packing Group II medium danger and Packing Group III low danger. Explosives, gases and radioactive material do not use packing groups; most of the remaining classes do.
The packing group decides how strong the packaging must be. UK guidance on dangerous goods packaging sets it out clearly: packaging approved for Packing Group I carries the code X and must survive a drop test from at least 1.8 metres, Group II carries Y with a 1.2 metre drop, and Group III carries Z with a 0.8 metre drop.
You can read this straight off a UN-marked box. A drum marked with Y can carry Packing Group II or III goods, never Group I. When a product meets the criteria for two packing groups, the most stringent one applies.
How Dangerous Goods Classes Work in Sea Freight
The IMDG Code applies to every ship carrying dangerous goods that falls under SOLAS, the international safety convention, whose Chapter VII holds the mandatory rules for carrying dangerous goods. The code is revised every two years. The current edition, Amendment 42-24, entered transitional effect on 1 January 2025 and is mandatory from 1 January 2026 to 31 December 2027, with new requirements for marking, packing and stowing lithium and sodium ion batteries.
What the Class Changes on a Shipment
In practice, the class drives four things on a sea shipment.
- Documentation. The dangerous goods transport document lists the UN number, proper shipping name, class and packing group for every item, and the carrier uses it to plan the stowage.
- Labels and placards. Each package carries the class label, and a container carries class placards of at least 250 mm by 250 mm on all four sides, the same minimum size US rules require.
- Segregation. The code's segregation provisions decide which classes may share a container or sit near each other on deck, keeping oxidizers, for example, away from flammable cargo.
- Stowage. Some classes must go on deck where a fire can be fought or a leak can vent, others below deck away from heat and living quarters.
This is also why a carrier may refuse a booking or roll a container to a later vessel: every ship has limits on how much of each class it can take and where. If your import includes declared dangerous goods, add the DG paperwork to your shipping documents checklist before the booking, not after.
Why Misdeclared Dangerous Goods Start Ship Fires
Declaring a cargo as dangerous costs more, and that cost tempts some shippers to call it something else. Allianz has reported that industry systems attribute around 25% of serious incidents on container ships to misdeclared dangerous goods such as chemicals, batteries and charcoal, and that some shippers label fireworks as toys to avoid the cost.
The numbers have not improved. Reporting on Allianz claims data, The Maritime Executive noted that a containership fire occurred every 17 days on average in 2025, and that more than 200 fire incidents on large vessels made it the second-highest total of the past decade. The marine insurers' association IUMI reports around 250 fire incidents in 2024 alone, with a notable share of serious onboard incidents linked to misdeclared dangerous goods.
A misdeclared container is dangerous twice: it is packed without the right protection, and it is stowed without the crew knowing what is inside. P&I club Gard has described lithium battery fires in cargo declared as "mobile phone accessories" and "solar chargers", and used electric vehicles declared simply as "cars" instead of under Class 9.
What a Ship Fire Looks Like on AIS
When a fire does break out, the ship's movements change immediately. In October 2026 the containership HMM Platinum broadcast "restricted manoeuvrability" on its AIS signal while diverting to South Africa after a container fire in the Indian Ocean. If you track a vessel carrying your cargo in Primo Nautic, that navigation status, the slower speed and the changed course show up in the live vessel data, and its delay detection flags that the arrival time no longer holds.
What Shippers and Importers Should Check
Most of the responsibility for a dangerous goods shipment sits with the shipper, the party that classifies and declares the goods. As an importer, you still carry the commercial risk when a container is held, rolled or damaged. A few checks cover most of it:
- Ask the supplier for the safety data sheet. Section 14 lists the UN number, class and packing group for transport, and it should match what goes on the booking.
- Check anything with a battery. Electronics, tools, toys and e-bikes often travel under lithium battery entries, and the exemption only covers small, well-packed batteries.
- Confirm the forwarder accepts the class. Not every forwarder or carrier handles every class, and explosives and radioactive material usually need a specialist.
- Review your insurance. Undeclared dangerous goods can void a claim, so read how your cargo insurance policy treats them.
Once the container is loaded, the remaining question is where the ship is and when it will arrive. Primo Nautic's Cargo Shipment purpose gives precise, logistics-focused updates on the vessel by name, MMSI or IMO number, with the captain's reported ETA next to an AI-calculated one, so a diversion or delay is visible early.
Key Takeaways on Dangerous Goods Classes
There are nine dangerous goods classes, set by the UN and used by every transport mode. The class names the type of hazard, divisions narrow it down, and packing groups I, II and III rank the danger within a class and set the strength of the packaging.
At sea, the IMDG Code turns the class into concrete duties: a dangerous goods transport document, labels and placards, segregation from incompatible cargo and the right stowage position. Amendment 42-24 is the edition in force through 2027, with tighter rules for lithium and sodium ion batteries.
The biggest risk is not the declared cargo but the undeclared kind. Misdeclared batteries, chemicals and charcoal remain a leading cause of container ship fires, and an accurate class on the booking is what lets the crew stow and fight a fire safely.
