The hazard class tells you what kind of danger a material poses. The packing group tells you how much danger within that kind. It is a second layer of detail that drives how a material must be packaged, and it shows up on shipping papers, so it is worth understanding even though it is not on the placard.
This is study guidance, not regulatory advice. The packing group for a material is listed in the Hazardous Materials Table in 49 CFR 172.101 and your official state CDL manual.
What the three groups mean
| Packing group | Degree of danger |
|---|---|
| PG I | Great danger |
| PG II | Medium danger |
| PG III | Minor danger |
The lower the number, the greater the danger, which is the same direction as hazard-class divisions. PG I materials need the most robust packaging; PG III the least.
Which classes use packing groups
Not every hazard class uses packing groups. Classes that have a range of severities, such as flammable liquids (3), flammable solids (4), oxidizers and organic peroxides (5), toxic substances (6.1), corrosives (8), and miscellaneous (9), use them. Classes 1 (explosives), 2 (gases), and 7 (radioactive) do not use packing groups, because they are categorized by other systems like divisions, label categories, and compatibility groups. For the class framework, see the nine hazard classes.
Where you see it
The packing group appears in the hazardous materials description on the shipping papers, alongside the proper shipping name, hazard class, and the four-digit identification number. It is part of how the document fully specifies the material and its required packaging.
Where it fits
Packing groups connect the hazard class to the packaging and documentation rules. For the federal framework, see the FMCSA hazardous materials regulations and the PHMSA hazmat resources. For the test, remember the simple ranking: PG I is the most dangerous, PG III the least.
Frequently asked questions
What are packing groups in hazmat?
Packing groups rank the degree of danger within certain hazard classes. PG I is great danger, PG II is medium danger, and PG III is minor danger. They drive packaging requirements and appear on shipping papers.
Which packing group is the most dangerous?
PG I is the most dangerous, requiring the most robust packaging. PG III is the least dangerous. The lower the number, the greater the danger.
Do all hazard classes have packing groups?
No. Classes 1 (explosives), 2 (gases), and 7 (radioactive) do not use packing groups; they use other systems such as divisions, label categories, and compatibility groups. Most other classes do use them.
What is the best way to study packing groups for the CDL test?
Learn the simple I-II-III danger ranking and where it appears on shipping papers, and keep your placard and class recognition sharp with an app such as CDL Placards. Your state CDL manual is the authority.
