Triple packaging exists so that liquid stays inside the box even if the primary receptacle breaks. UN 3373 applies to Category B biological substances: under ADR 2.2.62.1.4.2, any infectious substance that does not meet the Category A criteria. The category follows from where the specimen came from and which agent is suspected, and it is settled before the box is chosen.
The three layers are the primary receptacle, the secondary packaging and the outer packaging. For liquids, both the primary and the secondary are leakproof, absorbent material between them must be able to take up the entire contents, fragile tubes sharing one secondary are wrapped or separated, and either the primary or the secondary withstands an internal pressure of 95 kPa. For solids, both layers are siftproof. Road and air rules alike require one outer surface of at least 100 x 100 mm and a completed package that survives a 1.2 m drop in any orientation without leakage from the primary.
| Requirement | Road, ADR 2025 P650 | Air, IATA DGR 2026 PI 650 |
|---|---|---|
| Rigid layer | Secondary or outer packaging | Outer packaging |
| Liquid limits | Not set in P650 | 1 L per primary, 4 L per outer package |
| Solid limit | Not set in P650 | 4 kg per outer package |
| Itemized contents list | Not in P650 | Between secondary and outer packaging |
| Paperwork | No further ADR requirements | No Shipper's Declaration; name and phone of a responsible person on the air waybill or package |
When coolant is added. Ice or dry ice goes outside the secondary packaging, with interior supports that hold the secondary in place once the coolant has gone. With ice the outer packaging or overpack must be leakproof; dry ice brings in ADR 5.5.3 by road and the dry ice rules by air, and the package must let carbon dioxide escape. The primary and secondary must keep their integrity at the coolant's temperature and at the temperature and pressure that would follow if cooling were lost. The 4 L and 4 kg air limits exclude the coolant.