What Is a UN Number

Where Do UN Numbers Come From?

UN numbers are assigned by the UN Committee of Experts on the Transport of Dangerous Goods and published in the UN Recommendations on the Transport of Dangerous Goods — the Orange Book — which UNECE issues on a biennial cycle. Numbers run from UN 0004 to approximately UN 3550; entries UN 0001 through UN 0003 are retired. No UN number exists for substances that are not classified as dangerous.

The Orange Book is the source from which all four international transport mode regulations draw their substance classifications. ADR transport adopts it for European road freight. The IMDG Code applies it to sea freight. The ICAO Technical Instructions and IATA Dangerous Goods Regulations apply it to air. RID applies it to international rail. A consignment leaving Ghent by road to Rotterdam port and continuing by sea to Valencia carries the same UN number on the ADR road transport document and the sea freight bill of lading. UN number classification and the full terminology used across European road freight dangerous goods compliance are part of the documentation framework covered in the Go Trans logistics glossary.

What Information Does a UN Number Encode?

A UN number identifies the substance — it does not encode the hazard class. The hazard class, packing group, and transport conditions must all be looked up in ADR Table A using the number as the key; they cannot be read from the digits.

What ADR Table A returns for any UN number is the complete transport profile: proper shipping name, hazard class, classification codes, packing group where applicable, special provisions, limited quantity threshold, excepted quantity threshold, packaging instructions, and tank requirements. One row in Table A gives the full compliance picture for that substance on European roads.

Some UN numbers cover a group of substances rather than a single compound. UN 1993 — "Flammable liquid, n.o.s." — is a group entry for flammable liquids without individually assigned numbers. N.o.s. stands for "not otherwise specified." Group entries require the shipper to add the technical chemical name of the specific substance in brackets on the transport document.

The same chemical can carry different UN numbers depending on concentration or physical state. Acetic acid above 80% concentration is UN 2789; below 80% it is UN 2790. A substance in liquid state may have a separate UN number from its solid form when the hazard profile differs between states. Concentration and purity are classification variables, not fixed identifiers.

Where Does a UN Number Appear in European Road Freight?

UN numbers appear in four places on every ADR consignment: the transport document, package labels and marks, IBC markings, and the vehicle orange plate.

• The transport document carries the UN number as the first field of the complete dangerous goods description, in this exact format: UN number + proper shipping name + hazard class + packing group. A petrol consignment reads: "UN 1203, PETROL, 3, II." This four-part entry is mandatory on every ADR transport document and is the primary reference used by enforcement inspectors at any stop during transit. The shipping documents in European road freight — transport document, written instructions, Safety Data Sheet, and vehicle approval certificate — must all be present on every ADR consignment from collection point to delivery address.
• Package labels and marks display the UN number alongside the hazard class diamond and proper shipping name on the outer surface of every dangerous goods package.
• IBC and large packaging marks carry the UN number on intermediate bulk containers used for Class 3, 4, 5, 6.1, 8, and 9 goods transported above standard package volume thresholds.
• The orange plate — the Kemler plate — mounted front and rear on every ADR vehicle displays the UN number in the lower section. The upper section carries the Kemler hazard identification number, a 2- or 3-digit code indicating the primary hazard and any subsidiary hazard of the substance on board. Emergency services at an incident read the orange plate before accessing any cab document — the UN number and Kemler code together identify what is being carried and what emergency response applies.

What Are the Most Common UN Numbers in European Road Freight?

• UN 1203 — Petrol / Gasoline / Motor spirit — Class 3 — Packing Group II — is the highest-volume dangerous goods movement on European roads, ahead of all other UN numbers by tonnage on the continent.
• UN 1202 — Gas oil / Diesel fuel / Heating oil, light — Class 3 — Packing Group III. Standard fuel distribution across European road haulage networks.
• UN 1950 — Aerosols — Class 2 — no packing group. Common across FMCG and consumer goods supply chains; aerosols above the excepted quantity threshold require full ADR compliance including transport document and vehicle marking.
• UN 3480 — Lithium ion batteries — Class 9 — no packing group. Standalone batteries: electric vehicle packs, industrial energy storage units, consumer device batteries transported separately from equipment.
• UN 3481 — Lithium ion batteries contained in equipment / packed with equipment — Class 9 — no packing group. Consumer electronics, power tools, laptops, and medical devices with integrated battery systems.
• UN 1789 — Hydrochloric acid — Class 8 — Packing Group II or III depending on concentration.
• UN 2794 — Batteries, wet, filled with acid — Class 8 — no packing group. Lead acid batteries across automotive supply and industrial logistics.
• UN 1072 — Oxygen, compressed — Class 2.2 — no packing group. Medical oxygen distribution and industrial gas supply chains.
• UN 1170 — Ethanol solution / Ethyl alcohol solution — Class 3 — Packing Group II or III depending on concentration.

How Does a Shipper Find the Correct UN Number?

• The Safety Data Sheet Section 14 (Transport Information) is the primary source — the manufacturer or supplier states the UN number, proper shipping name, hazard class, and packing group for the substance there. When the SDS is current and correctly prepared, the complete dangerous goods description for the transport document is already available before the shipper opens ADR Table A.
• ADR Table A — the master substance list in ADR 2025 — is the definitive reference for European road freight classification. Every classified substance has a row in Table A with its UN number and full transport conditions. ADR 2025 is freely accessible through the UNECE website.
• For n.o.s. entries, the technical name of the specific substance must be placed in brackets after the proper shipping name on the transport document — identifying the correct n.o.s. entry comes first, then the technical name follows. A toluene consignment without its own assigned UN number is declared as: "UN 1993, FLAMMABLE LIQUID, N.O.S. (toluene), 3, II." The n.o.s. designation carries no compliance reduction — full ADR documentation, packaging, labelling, and vehicle marking requirements apply.
• Where classification is uncertain — mixtures, novel substances, or goods that span hazard class boundaries — a Dangerous Goods Safety Adviser (DGSA) provides classification guidance before the booking is placed.

What Is the Difference Between a UN Number, a CAS Number, and an HS Code?

A UN number classifies for transport safety, a CAS number identifies for scientific and laboratory purposes, and an HS code classifies for customs tariff and trade statistics — three parallel systems serving three separate regulatory authorities with no overlap in function.

• A UN number is required on the ADR transport document, package labels, and vehicle orange plates. It connects the substance to every dangerous goods compliance requirement: packaging standards, labelling, driver certification, and vehicle equipment. The hazard class is not embedded in the number — it is linked through ADR Table A.
• A CAS number (Chemical Abstracts Service registry number) is issued by the American Chemical Society. It identifies a specific chemical compound for laboratory, manufacturing, and regulatory reporting. It appears on the Safety Data Sheet but is not required on any transport document and carries no ADR obligations.
• An HS code (Harmonised System tariff code) is issued by the World Customs Organization. It classifies goods for duty assessment, import and export declarations, and international trade statistics. It is required on customs documents and has no connection to dangerous goods transport safety.

A consignment of hydrochloric acid from Antwerp to a German chemical plant needs all three simultaneously: UN 1789 on the ADR transport document and Kemler plate, the CAS number on the Safety Data Sheet, and the HS code on the customs transit declaration. Each number answers a different authority's question at a different point in the movement.