The IMDG segregation table is the 9-by-9 matrix in Chapter 7.2 of the IMDG Code that specifies how each dangerous goods class must be stowed in relation to each other class on a vessel and inside a cargo transport unit. The table is the operational reference for any freight forwarder, terminal operator, or buyer checking whether a mixed-DG shipment can stow together. The codes range from ‘1’ (away from) to ‘4’ (segregated longitudinally by an intervening complete compartment or hold), with ‘X’ meaning no general requirement and ‘Refer to specific provisions’ meaning the substance entry has its own rule.
The five segregation codes
| Code | Meaning |
|---|---|
| 1 | Away from. Effectively separated so an incident involving one cargo cannot involve the other. In a container: kept apart with reasonable spacing. |
| 2 | Separated from. In different holds or compartments. Cannot be in the same container even with separation. |
| 3 | Separated by a complete compartment or hold from. A complete intervening compartment between them. |
| 4 | Separated longitudinally by an intervening complete compartment or hold from. The strictest. |
| X | No general segregation requirement. See the specific entry in the IMDG list, the substance may have its own rule. |
The numbers escalate. A “1” is a routine handling instruction; a “4” effectively means the cargoes cannot share a single vessel deck.
How the table is structured
The table is organised by class and subclass:
| Class | 1 | 2.1 | 2.2 | 2.3 | 3 | 4.1 | 4.2 | 4.3 | 5.1 | 5.2 | 6.1 | 6.2 | 7 | 8 | 9 |
|---|
Read across a row to see how the row’s class must be stowed against each column class. The table is symmetric: Class 5.1 vs Class 3 reads the same as Class 3 vs Class 5.1.
High-conflict pairs in chemical sourcing
Several pairs come up routinely in mixed-DG container booking from China:
| Pair | Code | Reason |
|---|---|---|
| Class 3 (flammable liquids) vs Class 5.1 (oxidisers) | 2 (separated from) | Oxidisers can intensify a flammable-liquid fire |
| Class 4.1 (flammable solids) vs Class 5.1 | 2 | Same fire-intensification mechanism |
| Class 8 acids vs Class 8 bases | ”Refer”, see substance entries | Acid-base reaction risk if both leak |
| Class 5.2 (organic peroxides) vs Class 3 | 3 (separated by complete compartment) | Peroxides decompose violently when mixed with flammable liquids |
| Class 7 (radioactives) vs almost everything | 2 to 4 | Generic radioactive contamination control |
| Class 1 (explosives) vs almost everything | 2 to 4 | Explosive shock and contamination |
For containerised cargo, “Code 2” (separated from) effectively means the substances cannot share a container. A Class 3 LCL consolidation cannot include Class 5.1 LCL cargo in the same container, the forwarder must split into two containers.
The within-class rules
The table addresses inter-class segregation. Within a class, individual substances can have their own rules:
- Within Class 8 (corrosives): acids and bases must be segregated from each other. A drum of sulphuric acid (UN 1830) cannot share a pallet with a drum of sodium hydroxide solution (UN 1824) in the same container.
- Within Class 5.1 (oxidisers): chlorate-based oxidisers must be segregated from many organics within the same class.
- Within Class 6.1 (toxics): cyanide-based toxics must be segregated from acids, cyanide salts release hydrogen cyanide gas on contact with acid.
These within-class rules are in the substance-specific entries in the IMDG list, columns 16a (segregation) and 16b (stowage). Always check the per-substance rules in addition to the table.
How to verify a mixed-DG container before booking
Five-step check:
- List every UN number going into the container with class, subclass, PG, and quantity.
- Build the pairwise segregation requirement for each combination from the table.
- Cross-check each substance’s own column 16 entry for substance-specific rules beyond the table.
- Apply the within-class rules for Class 5.1, Class 6.1, and Class 8 internally.
- Confirm with the carrier, the carrier’s hazmat desk runs the same check and will refuse mismatched bookings.
For complex mixed loads, pesticide formulators shipping 4 to 8 different active ingredients in one container, this check takes 30 to 60 minutes per container. Routine, but not skippable.
The DG classifier tool gap
The 9-by-9 segregation matrix is public domain (from IMDG Volume 1, Chapter 7.2). A free online tool that takes two UN numbers and outputs the segregation requirement would save every forwarder, importer, and terminal hazmat desk time on every mixed-DG booking. Sourzi’s planned DG classifier tool is built on this matrix.
Operator note: the carrier-specific layer
Carrier policies sometimes go beyond IMDG segregation. Some carriers refuse certain class combinations regardless of what the table allows. Maersk, MSC, and Hapag-Lloyd each maintain their own DG acceptance matrices that overlay IMDG. A booking accepted under IMDG but refused under carrier policy is a routine booking failure. Always cross-check with the actual carrier’s hazmat desk before assuming the cargo will load.
Related terms
IMDG umbrella code. The class-specific entries, Class 3, Class 5.1, Class 8, each list the segregation conflicts that matter most for that class. Marine pollutant cargoes have additional stowage rules on top of segregation.