UN number

A UN number is the four-digit identifier assigned to a dangerous substance or article under the UN Recommendations on the Transport of Dangerous Goods (the Orange Book), maintained by the UN Sub-Committee of Experts. It is the common key linking the IMDG Code for sea, ADR for road, RID for rail, and the ICAO/IATA rules for air, so the same UN number identifies the hazard across every mode. It drives the proper shipping name, the placarding, and the packing and segregation requirements applied to the consignment.