The Packing Group (PG) is a three-tier classification within most dangerous-goods classes that indicates the relative severity of the hazard. PG I is the most hazardous, PG II medium, PG III minor. Not all DG classes use packing groups. Class 1 (explosives), Class 2 (gases), and Class 7 (radioactive) have their own systems, but for the chemical classes most relevant to industrial sourcing (3, 4, 5.1, 6.1, 8, 9), the packing group is part of the cargo’s identity and dictates how it must be packed.
What the packing group determines
Three things scale with packing group:
- Packaging performance requirements. PG I packaging must withstand a 1.8 metre drop test (for liquids, depending on density). PG II requires 1.2 metres. PG III requires 0.8 metres. Each test corresponds to a UN packaging certification level. X for PG I, Y for PG II, Z for PG III. The drum or IBC carries a UN code stamp showing the level it has been tested to.
- Regulatory paperwork load. PG I shipments attract more regulatory attention, more carrier scrutiny, and sometimes vessel routing restrictions. PG III moves with substantially less friction.
- Insurance premium. Marine cargo insurance for PG I and PG II cargo is higher than for PG III, even within the same DG class.
How packing group is assigned
The packing group is determined by the substance’s intrinsic properties, not by the importer’s preference. For Class 3 flammable liquids, packing group is set by flashpoint and initial boiling point. For Class 6.1 toxics, by oral, dermal, and inhalation toxicity. For Class 8 corrosives, by skin destruction time. The IMDG Code provides the criteria for each class and the test methodology.
Common PG misclassification failures
The most expensive failure mode we have seen across twenty years: factory provides PG III packaging (Z code) for a substance that the destination authority subsequently classifies as PG II. The cargo arrives, the destination port inspects, finds the packaging UN code does not match the required PG level, and the cargo is held until repackaging at destination. Repackaging a 20-foot container of corrosive into PG II drums at the destination port is a five-figure problem and weeks of delay.
The reverse, using PG II packaging for a PG III substance, is technically over-spec and not illegal, but the importer pays more for packaging than necessary.
How we verify before shipment
Before any DG container loads, we verify three places carry the same packing group:
- DG Declaration Box for packing group
- MSDS Section 14
- UN code stamp on the actual packaging, the second character of the UN code (X, Y, or Z) corresponds to the highest PG the packaging has been tested for. A UN code of “1A1/Y1.4/250/24/CHN/12345” indicates a 1A1 steel drum tested to PG II (Y) at 1.4 specific gravity and 250 kPa hydrostatic pressure, manufactured in China by registered facility 12345 in 2024.
We photograph the UN code stamp on a sample of drums during the SGS pre-shipment inspection and verify it matches the assigned packing group on the DG Declaration. If the code stamp shows Z (PG III) and the DG Declaration says PG II, we hold the cargo until the factory either re-packages or re-evaluates the packing group with documentation.
Practical sourcing notes
For a first-time order of any DG substance, ask the factory to confirm three things on the quote: the UN number, the packing group, and the UN code stamp on the proposed packaging. Get those three in writing before the deposit is paid. Errors caught at quote stage are free; errors caught at the destination port are catastrophic.
Related terms
IMDG defines the packing groups for each DG class. DG Declaration and MSDS Section 14 must both carry the assigned PG. UN Number and packing group together identify the cargo for the carrier and the port.