An overpack is an enclosure — shrink-wrap, a pallet, a box or a crate — used to contain one or more packages consolidated into a single unit that is easier to handle and stow during carriage (1.2.1). For radioactive material the definition adds that it is used by a single consignor. A shrink-wrapped pallet of twenty drums is an overpack, and so is a cardboard tray holding four small boxes for one consignee. A freight container is not — ADR treats it as a container in its own right (1.2.1), with its own placarding rules.
When overpack markings apply (5.1.2.1). If the marks and labels of Chapter 5.2 representative of all the dangerous goods inside are not visible through the outer layer, the overpack itself must carry the following.
- The word
OVERPACKin lettering at least 12 mm high, in an official language of the country of origin (plus English, French or German if none of those is official) - The UN number of each item of dangerous goods inside, prefixed
UN— 12 mm high as a rule, 6 mm for packages of 30 L or 30 kg or less (5.2.1.1) - Each hazard label corresponding to each item inside — primary and subsidiary
- The other marks required for packages by Chapter 5.2, such as the environmental hazard mark and the battery mark. The marks of 5.2.1.3 to 5.2.1.6 (including
SALVAGE), 5.2.1.7.2 to 5.2.1.7.8 and 5.2.1.10 are expressly excluded. Each applicable mark or label only needs to be applied once
If the marks and labels representing all the goods inside remain visible through the outer wrap, nothing has to be added to the overpack. Orientation arrows are the separate case — an overpack containing packages that must bear them carries the arrows on two opposite sides unless the arrows on the packages themselves stay visible (5.1.2.1 (b)).
Mixing. An overpack may contain different UN numbers provided the substances are permitted to travel together — the prohibitions on mixed loading of 7.5.2 apply to overpacks as well (5.1.2.4). Each package inside must still comply with all applicable provisions of ADR, and the overpack must not impair the function of any of them (5.1.2.2).
Transport document. The transport document must list every UN number present on the vehicle, including those grouped inside overpacks. Overpack is a handling convenience, not a way to aggregate entries.
Common mistake — treating a shrink-wrapped pallet as a single package and declaring one UN number for the whole load on the transport document. The inspector opens the wrap and finds three different UN numbers — misdeclaration, and the consignment is stopped.
References — ADR 2025 1.2.1 (definition of overpack), 5.1.2.1 (overpack marking), 5.1.2.2 (packages inside), 5.1.2.4 (mixed loading), 5.2.1 (package marking inherited by the overpack), 7.5.2 (mixed loading prohibitions).