A four-digit number, assigned by the UN, that identifies a dangerous substance or article in transport — e.g. UN3480 for lithium-ion batteries shipped alone. It pairs with a proper shipping name and drives the packing, marking and documentation that apply. The right UN number is the starting point of every DG shipment; the wrong one invalidates the whole declaration.
Full guideWhat is Class 9, and why so much freight ends up in it →