Dangerous Goods in Container Loading: Segregation Made Simple

Quick answer: When a shipment contains dangerous goods (DG) — flammables, oxidisers, corrosives, toxics and so on — you can’t just pack them wherever they fit. International rules (the IMDG Code for sea freight) define segregation requirements that keep incompatible classes apart: some must be “away from” each other, some “separated from”, and some can’t share a container at all. Load them together anyway and you risk a rejected booking, a fine, or — in the worst case — a reaction, leak or fire in a sealed steel box in the middle of an ocean.

The good news: segregation is a rules problem, and rules problems are exactly what a load planner can enforce. Here’s the model, and how to keep incompatible cargo separated without doing the table lookups by hand every time.

Keep incompatible groups apart automatically. Tag cargo into groups that must not mix, and ContainerMath’s plan-level segregation rules keep them in separate containers when they can’t share one. Free to try, no card.

Plan a segregated load — free trial →

Why segregation exists

Dangerous goods are classified into hazard classes (Class 1 explosives, Class 3 flammable liquids, Class 5.1 oxidisers, Class 8 corrosives, and so on). The danger isn’t only each cargo on its own — it’s what happens when two incompatible classes meet. An oxidiser leaking onto a flammable is a fire. A corrosive attacking a compressed-gas cylinder is a rupture. Segregation rules exist so that a single packaging failure doesn’t cascade into a catastrophe inside a container nobody can reach until the ship docks.

The four segregation levels (IMDG)

The IMDG Code’s segregation table reduces the relationship between any two classes to one of four outcomes:

Level	Meaning
Away from	Kept apart, but may share a container with a minimum separation
Separated from	Not in the same container section; typically different containers or well-separated
Separated by a complete compartment or hold from	Stronger separation still
Prohibited	Must never be loaded together

For containerised freight the practical takeaway is simple: certain class pairs cannot share a container, and others need documented separation. Which pairs depends on the exact UN numbers and classes — that’s what the segregation table encodes.

Where DIY planning goes wrong

Teams shipping mixed DG loads usually manage segregation with a printed table, a spreadsheet, and a lot of care. The failure modes are predictable:

• A missed pair. One SKU’s class is overlooked and two “separated from” goods end up in the same box.
• Re-checking every revision. A quantity change or a new line item means re-running the whole table by hand — so people skip it under time pressure.
• No link to the actual load plan. The segregation check lives in one document and the stuffing plan in another; nothing enforces that the plan honours the check.

Every one of these is a manual step that a load plan can absorb — if the planner understands “these groups must not share a container.”

Segregate by planning it in, not checking it after

The reliable way to handle DG segregation is to make it part of the load plan itself, so incompatible cargo is never placed together in the first place rather than caught in a review afterward.

That’s what plan-level segregation rules do in ContainerMath: you assign cargo to groups that must be kept apart, and the packing engine keeps those groups in separate containers when they can’t share one — automatically, on every recalculation, including after you change a quantity or add a SKU. The 3D plan then reflects a stow that already respects the rule, and the compliance view surfaces the relevant advisories alongside the axle and weight checks so the whole load is reviewed in one place.

Important: ContainerMath’s segregation rules help you plan a load that keeps groups you define apart — they’re a planning aid, not a substitute for a qualified DG declaration, the current IMDG Code, or your carrier’s acceptance rules. Always confirm the specific requirements for your UN numbers with your DG advisor and carrier.

Plan the separation in from the start

Dangerous-goods segregation is a rules problem, and doing rules by hand on every shipment is where mistakes creep in. ContainerMath is container loading software that lets you define groups which must not mix and keeps them in separate containers as it packs — so a compliant stow is the default output, not an afterthought. Combined with per-item handling flags and full weight-and-axle checks, it plans the whole load — hazardous and not — in one pass.

Keep incompatible cargo apart — free →

Frequently asked questions

What is dangerous goods segregation?

Segregation is the set of rules that keep incompatible dangerous goods apart during transport so a leak or failure in one can’t react with another. For sea freight the IMDG Code defines, for every pair of hazard classes, whether they can share a container, must be separated, or must never be loaded together.

What are the IMDG segregation levels?

Four: “away from” (kept apart with minimum separation, may share a container), “separated from” (not in the same container section), “separated by a complete compartment or hold from” (stronger separation), and prohibited (never loaded together).

Can dangerous goods of different classes go in the same container?

Sometimes — it depends entirely on the specific classes and UN numbers. Some pairs may share a container with separation (“away from”), others must be in different containers (“separated from”), and some combinations are prohibited outright. The IMDG segregation table defines which is which.

How does ContainerMath handle dangerous goods segregation?

You assign cargo to groups that must be kept apart, and the packing engine keeps those groups in separate containers when they can’t share one — automatically, on every recalculation. It’s a planning aid that enforces the groups you define; it doesn’t replace a qualified DG declaration, the IMDG Code, or your carrier’s acceptance rules.

Is software enough to stay compliant with dangerous goods rules?

No — software helps you plan a load that respects the segregation groups you define and flags issues early, but final compliance still needs a qualified DG declaration, the current IMDG Code, and your carrier’s acceptance rules. Use the plan to get it right up front, and confirm specifics with your DG advisor.