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Dangerous Goods Classes & Segregation Explained (On Board)

Understand the nine DG classes and the four segregation levels on board — from "away from" to longitudinal separation by a whole hold — with interactive diagrams.

Four segregation levels

Level 2 · Separated from

Separated

Under deck the two loads must be in different compartments or holds; a fire- and watertight deck between them counts as the separation.

Under deck

Different holds/compartments (may be adjacent, divided by a bulkhead or deck).

On deck

On deck a larger horizontal distance is enough (about 6 m is quoted for conventional cargo).

Schematic diagram

Hold 1Hold 2Hold 3Hold 4Hold 5AB

adjacent holds — Different holds/compartments (may be adjacent, divided by a bulkhead or deck).

DG classes and their main consideration

Class 1

Explosives

Most restrictive towards almost every other class; among class 1 itself the compatibility group rules apply.

Class 2

Gases

Pressure and fire (2.1) or toxic (2.3) hazards; keep flammable gases away from heat and from oxidizers.

Class 3

Flammable liquids

Vapours can ignite: separate from oxidizers (5.1), organic peroxides (5.2) and explosives.

Class 4

Flammable solids, spontaneously combustible, water-reactive

4.3 gives off flammable gas when wet: keep away from water and liquids; 4.2 can self-heat.

Class 5

Oxidizers & organic peroxides

Feed a fire: keep away from combustibles; many organic peroxides need temperature control.

Class 6

Toxic & infectious

Key principle: keep away from foodstuffs and feed; 6.2 has special packaging requirements.

Class 7

Radioactive

Distance from crew, undeveloped film and other cargo is governed by the transport index (TI) and dose limits.

Class 8

Corrosives

Acids and alkalis react with each other; many corrosives also react with metals or water.

Class 9

Miscellaneous (incl. lithium batteries)

Usually no general segregation requirement, but specific entries (e.g. lithium batteries) have their own stowage provisions.

Steps to check DG segregation

  1. Identify each item: UN number, proper shipping name, class, subsidiary hazard, packing group (from the DG declaration and SDS).

  2. Read the entry in the Dangerous Goods List of the IMDG Code edition in force: stowage category, stowage/handling codes and specific segregation codes.

  3. Apply the general segregation between classes (including subsidiary hazards), then the entry-specific provisions and segregation groups (e.g. acids vs alkalis).

  4. Translate the segregation level into real positions for the ship type (container, general cargo, ro-ro) and on-deck/under-deck stowage.

  5. Check carrier and port restrictions (prohibited classes, quantity limits, special approvals) and the ship’s Document of Compliance.

DG classes & labels guideUN number lookup
This page deliberately contains no IMDG segregation table or distances per ship type (IMO copyright). Detailed segregation checks are available in the Vessel Planner with licensed data.

About this calculator

Dangerous goods (DG) that are incompatible with each other must not be stowed close together: oxidizers can feed a fire in flammable liquids, acids react with alkalis and toxic substances must stay away from foodstuffs. Segregation is how a ship makes sure that a leak or fire in one cargo does not trigger a hazard in another.

This page explains the concepts in our own words. First, the nine DG classes and the main consideration for each when choosing a position. Second, the four segregation levels from the loosest to the strictest: away from (kept apart, may share a hold with a minimum distance), separated from (different holds or compartments), separated by a complete compartment or hold from (a whole hold in between) and separated longitudinally by an intervening complete compartment or hold from (a whole hold in between in the fore-and-aft direction). Interactive diagrams show what each level means under deck and on deck.

Third, the planner's line of thought: identify the UN number and class, read the Dangerous Goods List entry, apply general segregation and the entry-specific provisions, translate that into real positions for the ship type, then check carrier and port restrictions. This page deliberately contains no IMDG segregation table or distances per ship type — that data is IMO copyright. Detailed segregation checks are available in the Vessel Planner with licensed data. For classes and labels, see the dangerous goods classes guide.

Worked example

Schematic diagram of a five-hold ship, load A in hold 2 (index 1 from aft):

  • Away from (level 1): B in the same hold with a minimum horizontal distance
  • Separated from (level 2): B in the next hold, divided by one bulkhead
  • Separated by a complete compartment or hold (level 3): one whole hold between A and B (vertically or horizontally)
  • Separated longitudinally (level 4): one whole hold in between fore and aft; vertical separation alone is not enough

How to use it

  1. Choose a segregation level

    Click one of the four levels to see its meaning and a diagram of the positions of two loads A and B.

  2. Compare deck and hold

    Switch between under deck and on deck to see how separation differs.

  3. Learn the classes

    Read the main consideration for each class 1–9, then open the DG classes guide for labels and examples.

  4. Follow the check steps

    Use the list of steps as a checklist before accepting or placing DG in a plan.

Frequently asked questions

Why is there no segregation table on this page?
The IMDG Code text and tables are IMO copyright. STOWAGE.ID uses DG data only from licensed sources or customer rule sets inside the app. This public page teaches the concepts so you can read the official IMDG Code correctly.
Does the subsidiary hazard count for segregation?
Yes. Goods with a subsidiary hazard must be segregated according to both the primary class and the subsidiary; the strictest requirement applies. On top come entry-specific provisions and segregation groups such as acids and alkalis.
How does segregation work on container ships?
The principle is the same but translated into distances in container slots, bays and hold or deck positions, including rules for closed and open containers. The details are in the container ship part of the IMDG Code.
Who is responsible for segregation?
The shipper must declare DG correctly; the carrier and planner place it according to the rules; the master approves the DG stowage plan. Misdeclaration is a common cause of container fires.

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