IMDG Segregation Terms Explained

IMDG Segregation Terms Explained

IMDG Segregation: What the Terms Really Mean

Maybe I am not the only one who was confused by the terms in Section 7 of the IMDG Code. One of the most important things I discovered is that segregation within a cargo transport unit is not the same as segregation aboard a vessel. I hope you find it helpful. Understanding that distinction is essential when preparing dangerous goods shipments for ocean transport.

Why Segregation Matters

When shipping dangerous goods by ocean, one of the most misunderstood concepts is segregation. The IMDG Code uses simple phrases like “away from” and “separated from,” but those terms carry very specific operational meaning. If misunderstood, they can lead to improper stowage, rejected shipments, or worse — dangerous chemical interactions during transport.Under IMDG 7.2.3.2.2, dangerous goods subject to an applicable segregation requirement generally must not be packed together in the same cargo transport unit (CTU), unless a specific exception permits it.

The key is not just knowing the words but understanding how they translate into real-world loading decisions inside a container or on a vessel.

Segregation Code 1: Away From

Let’s start with the most common level: “away from.” This is segregation code 1, the least restrictive. For vessel stowage, it generally requires enough separation to prevent incompatible dangerous goods from interacting in an incident. The precise arrangement depends on the type of stowage and the applicable segregation provisions. However, this does not mean that a shipper can place incompatible dangerous goods on opposite ends of the same freight container. Separate pallets, dunnage or additional space between packages do not automatically satisfy the IMDG requirements for packing dangerous goods within a CT. The important distinction: “Away from” does not automatically mean “permitted in the same container.

Segregation Code 2: Separated From

The next level is “separated from,” or segregation code 2. This is where things become more restrictive. “Depending on the vessel’s stowage arrangement, this may involve separation by compartments, holds or prescribed distances. For a shipper preparing a freight container, however, the practical consideration remains the same: dangerous goods subject to this segregation requirement generally cannot be packed together in the same CTU. A partition or barrier installed inside a conventional freight container does not, by itself, provide an exemption from the segregation requirements.

Segregation Code 3: Separated by a Complete Compartment or Hold From

Moving up, we have “separated by a complete compartment or hold from,” which is segregation code 3. It involves separation by a complete compartment or hold, or other arrangements expressly permitted by the applicable IMDG provisions. The specific requirements depend on whether the dangerous goods are stowed on deck or under deck and on the vessel’s configuration. For shippers, the important point is that this segregation term cannot be satisfied merely by separating packages within a freight container.

Segregation Code 4: Separated Longitudinally by an Intervening Complete Compartment or Hold From

Finally, the most restrictive level is “separated longitudinally by an intervening complete compartment or hold from,” or segregation code 4. Sections 7.2.6 and 7.3.4 contain provisions that may permit certain dangerous goods to be packed together despite an otherwise applicable segregation requirement. However, these are not general exemptions. They have specific conditions that must be satisfied, and certain arrangements require competent-authority approval. The person responsible for packing the CTU must have sufficient information about the dangerous goods involved to determine whether an exception is applicable. This becomes particularly important with consolidated shipments containing dangerous goods from different shippers. For example, one shipper may have no knowledge of the chemical characteristics of another shipper’s products. Without adequate information, it may not be possible to establish whether the conditions for an exception have been met. The practical approach is to treat an applicable segregation requirement as prohibiting packing in the same CTU unless a specific IMDG provision clearly authorizes the arrangement.

The Impact of Subsidiary Hazards

What makes segregation particularly important is that it is driven not just by primary hazard classes, but also by subsidiary hazards. A product that appears compatible at first glance may trigger stricter segregation due to an additional hazard, such as an oxidizing or toxic subsidiary class. This is why classification is so critical — it directly determines how a shipment can be built.

Applying Segregation Rules in Real-World Shipping

When preparing dangerous goods for ocean transportation, I recommend asking two separate questions.

First: Can these dangerous goods be packed together in the same cargo transport unit? This requires checking the applicable segregation requirements and determining whether any specific exception permits the combination. Second: If the dangerous goods are in separate cargo transport units, how must those units be segregated aboard the vessel?  This is where the four segregation terms and the relevant vessel stowage provisions become particularly important. Keeping these questions separate helps avoid a common mistake: assuming that the distances or structural separation permitted aboard a vessel can also be applied inside a freight container.

Final Thoughts

At its core, IMDG segregation follows a simple progression: first, you separate by space, then by structure, and finally by distance across the vessel. When explained clearly, these rules are not just regulatory requirements — they are practical tools to prevent dangerous interactions at sea.

Confused about IMDG segregation requirements? ICC Compliance Center can help! Strengthen your knowledge with our IMDG training courses or contact our team to learn how we can support your dangerous goods shipping needs.

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