Packing group

Packing groups are used in the DOT hazmat rules in 49 CFR Parts 171-180 and in the international dangerous goods codes. Not every hazard class uses them. Explosives and most gases, for instance, are not assigned packing groups, while flammable liquids, many toxic materials, corrosives and several others are.

The numeral is a quick way to rank risk inside a class. Within Class 3 flammable liquids, a liquid that ignites very easily and boils at a low temperature is more dangerous in transport than one that needs warming before it ignites, so the first would receive a lower numeral, meaning a higher level of danger. Each class has its own criteria for how the group is decided, and the detailed cut-offs are set in the regulations rather than on the SDS.

Packaging is matched to the group. Containers are tested and marked to show which packing groups they can be used for, so a drum approved for Group III may not be acceptable for a Group I material. This is why a shipper cannot reuse any available container simply because the chemical is the same, and why substituting a cheaper container can make a shipment non-compliant.

The packing group appears on shipping papers after the UN number, proper shipping name and class. Together with the DOT hazard class, it is also used to look up exceptions such as Limited quantity allowances.