What Is a UN Number?
A UN number is the four-digit code that identifies a specific hazardous material for shipping worldwide. Here's what the numbers mean and how they're assigned.
A UN number (sometimes called a UN ID number) is a four-digit code — like UN1090 for acetone — that identifies a specific hazardous material or class of materials for transport purposes, recognized internationally. It's assigned by a United Nations committee of transport experts and used the same way in the U.S. Hazmat Table, European ADR regulations, and the IMO's shipping code, so the same material carries the same number no matter which country it's shipped through.
Why they exist
Before UN numbers, every country had its own way of naming and classifying dangerous goods, which made international shipping a mess — the same drum of chemical might need a completely different label depending on which border it crossed. The United Nations Committee of Experts on the Transport of Dangerous Goods standardized this in the 1950s, and the numbering system has been maintained and expanded ever since.
What the number actually tells you
A UN number by itself doesn't tell you the hazard class, packing group, or any shipping requirements — it's just an identifier. You always need to look up the number (or the material name) in the Hazmat Table to get the classification. For example, UN1090 is Acetone, hazard class 3 (flammable liquid), packing group II. The "1090" part is fixed; everything else is looked up separately.
Numbers are grouped loosely by hazard type and roughly by when they were added — UN0001 through UN0499 are mostly explosives, UN1001 and up covers most flammable and toxic substances, and newer or more specific entries tend to have higher numbers. There's no rule requiring related chemicals to have sequential numbers.
UN vs. NA numbers
You'll sometimes see "NA" instead of "UN" in front of a four-digit code — for example, NA1993 for a fuel oil blend. NA numbers are a U.S.-only extension used for materials that don't have an international UN number, or where U.S. rules need a distinct entry from the international one. NA numbers aren't recognized outside North America, so a shipment identified only by an NA number generally can't be exported under that identification — it needs to be re-classified under an equivalent UN entry first.
Where the number has to appear
The UN/NA number shows up in a few required places on an actual shipment:
- On the shipping paper, immediately before or after the proper shipping name (e.g., "UN1090, Acetone, 3, PG II").
- On placards for bulk shipments and certain quantities — the familiar diamond-shaped placard often has the UN number printed in the center or on an adjacent orange panel.
- On the package itself for many packing groups and quantities, per the marking requirements in 49 CFR Part 172, Subpart D.
A common mistake
People sometimes assume that if two products share a UN number, they can be shipped identically. That's not necessarily true — the same UN number can cover a range of concentrations, physical states, or packing groups (acetic acid solutions at different concentrations, for instance, can fall under different UN numbers or different packing groups within the same number). Always confirm the packing group and any special provisions for your specific product, not just the UN number.