Dangerous goods: UN numbers and IMDG classes

Hazardous cargo adds two coded fields to each item on a CSN, and they have to agree with each other. Customs rejects on the disagreement specifically, so getting one right and the other approximately right is the failure worth avoiding.

Which two fields?

Both are per item, not per consignment. A house bill carrying three commodities where only one is hazardous declares the UN number on that item alone; the other two carry the not-hazardous sentinels.

What do I put when nothing is hazardous?

ZZZZZ in the UN field and ZZZ in the IMDG field. Not blank.

This trips people up because "no dangerous goods" feels like an empty field. The MIG is explicit that ZZZ is to be declared when goods are not hazardous, and a real accepted filing carries exactly that. In this platform, picking "Not hazardous" fills both.

Where does the IMDG class come from?

From the UN number. Every UN number has exactly one class in the Dangerous Goods List — UN1203 (petrol) is class 3, UN1830 (sulphuric acid) is class 8 — so the class is not an independent judgement you make. Enter a recognised UN number and this platform fills the class for you.

If you change the class afterwards so that the two no longer agree, you get a warning rather than a block: the shipping document you are working from is the authority, and there are edge cases. But a disagreement is much more often a mistake than an edge case, and customs checks it:

Two codes for the same disagreement, read from each side. If you see either, do not adjust one field to silence it — check both against the dangerous goods declaration for the shipment.

Can I give the class without the division — 2 rather than 2.1? The guide's own list allows it: it carries 2, 4, 5 and 6 beside their divisions. The platform accepts them (until 25 September 2026 it refused them, offering only the divisions). A class is not treated as disagreeing with a UN number of one of its divisions. The division is still the more exact answer when you have it, and it is what the Dangerous Goods List gives.

Which list do the proper shipping names come from?

The IMDG Code — the International Maritime Dangerous Goods Code, which is the dangerous goods regime for sea transport and therefore the one that applies to a CSN.

This matters more than it sounds, because several national lists cover the same UN numbers with different wording. The clearest example is UN1203:

IMDG: MOTOR SPIRIT or GASOLINE or PETROLUS 49 CFR: Gasoline includes gasoline mixed with ethyl alcohol, with not more than 10% alcohol

Same substance, same UN number, different proper shipping name. Search results and safety data sheets prepared for a US shipment will show you the second one. For a filing to Indian customs for sea carriage, the IMDG wording is the correct one.

The hazard class can differ in shape too: the US table writes explosives as 1.1D, carrying the compatibility group letter, where the CSN's IMDG field wants 1.1.

What if my UN number is not in the list?

Check the number itself first — UN numbers are four digits and a transposed pair usually lands on another real substance rather than on nothing.

If the number is right and the platform does not offer it, the list may predate the amendment that introduced it. The IMDG Code is revised on a two-year cycle and new UN numbers are added each time; a list is a snapshot of one amendment.

Where this list stops: it carries 2,347 entries and runs to UN 3560, the last number assigned. Until 25 September 2026 it stopped at UN 3489 and this page said there was nothing above it — which was wrong: the UN Model Regulations, which the IMDG Code follows, have added numbers well past 3500 — sodium-ion batteries (3551, 3552), adsorbed gases (3510–3526), articles containing dangerous goods (3537–3548), vehicles powered by lithium or sodium batteries (3556–3558), medical waste (3549) and more. Those are on the list now, with their class. Two numbers in that range, 3492 and 3493, have been withdrawn and are not offered. A number newer still — the Code is revised every two years — may not be here yet; check the number itself against your shipper's declaration.

Not finding it does not stop you filing. The field accepts what you type; the list is a lookup that confirms the number and fills the hazard class for you, not a gate. What you lose on a number outside it is the confirmation and the automatic class, so set the IMDG class yourself from your shipper's declaration. It is worth telling us, because a gap affects everyone filing that commodity.

Is there a free official list I can check against?

Not for IMDG. The IMDG Code is published by the IMO as a priced publication, and the UN Model Regulations it derives from are issued as documents rather than as data. Public "IMDG" datasets that turn up in search results are usually the hazard-class table — twenty-odd rows explaining what class 3 means — rather than the Dangerous Goods List of several thousand substances.

The nearest free, authoritative, machine-readable equivalent is the United States' Hazardous Materials Table (49 CFR 172.101), which is public domain and covers most of the same UN numbers. It is genuinely useful for checking that a UN number exists and what class it carries. It is not a substitute for the proper shipping name, for the reason in the section above.

Related

Packing and quantity fields sit alongside these on the same item — see the field reference.If a filing is rejected on 33, 119 or 120, the rejection reasons page covers what to change and what not to.