What Are Hazmat Packing Groups?

Not all “hazardous materials” are equally hazardous. Most of the Hazard Classes and Divisions 1—9 cover a range of materials that, while they share a primary hazard, each have their own properties, ingredients, etc. For example: Some Class 8 corrosive materials present a very severe potential hazard (e.g., sulfuric acid), while others pose less severe risks (household cleaning products).

This is why hazmat "packing groups" are essential, and why being able to determine the PG for a material is a must-have skill to ensure shipments are properly classified, packaged, described on shipping papers, etc. to comply with the US DOT Hazardous Materials Regulations (HMR) and international standards (e.g., ICAO/IATA, IMDG Code). 

Definition of Packing Group (49 CFR 171.8)

The HMR defines packing group to mean "a grouping according to the degree of danger” for hazardous materials (49 CFR 171.8). Packing Group is commonly shortened to “PG,” including when used on hazmat shipping papers.  

A hazmat packing group (PG) has a twofold purpose: 1) To communicate the degree of danger and 2) to determine the strength of packaging required to contain the material in transportation. 

PG indicates the degree of danger for the material compared to others in the same class/division:  

• PG I indicates great danger
• PG II indicates medium danger
• PG III indicates minor danger

The packing group of a hazardous material correlates to a packaging performance level (X, Y, or Z) for certified UN or DOT specification packagings, as follows: 

• X-rated packagings are strong enough to hold PG I, PG II, or PG III materials.
• Y-rated packagings may be used to ship PG II or PG III materials. Not PG I. 
• Z-rated packagings may be used for PG III materials only 

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Which Classes/Divisions Have Packing Groups?

Most of the 9 hazard classes and divisions of regulated hazardous materials use PG I, II, and III to communicate severity of hazard. The video below shows how PG is determined for each class or division, including the criteria used to assign materials to the appropriate group.

These hazard classes/divisions are divided into PG I, II, and III: 

• Class 3—Flammable liquids
• Division 4.1*, 4.2, and 4.3—Flammable/reactive solids 
• Division 5.1—Oxidizers 
• Division 6.1—Poisons
• Class 8—Corrosives 
• Class 9—Miscellaneous (Some materials only) 

*Except self-reactive materials in Division 4.1

What About Other Hazard Classes and Divisions?

What about the rest of the 9 hazard classes and divisions regulated in transportation? The other classes and divisions also cover many different hazardous materials that can vary greatly in the severity of the hazard they pose. 

For some hazard classes and divisions, three categories of severity—PG I, II and III—are not adequate to communicate the full range of hazards represented in the class or division. In other cases, three categories are more than are needed. 

Instead of using packing groups, these classes and divisions are separated into “categories,” “hazard zones,” or other groupings to denote severity of hazard: 

• Divisions 1.1—1.6 (Explosives)*  
• Division 2.3 (Poison Gases) 
• Self-reactive materials in Division 4.1
• Division 5.2 (Organic Peroxides) 
• Division 6.2 (Infectious Substances) 
• Class 9—Miscellaneous (Some materials only)  

*Explosives in Class 1 are divided into thirteen compatibility groups that represent the degree of danger as well and prevent certain explosives from being transported together or with other incompatible materials. 

Division 2.1 and 2.2 Gases 

Flammable gases (Division 2.1) and Non-flammable gases (2.2) are not grouped by severity of hazard. These gases are transported in UN-specification cylinders that are engineered, tested, and regularly certified to contain any type of gas inside. 

Class 7—Radioactive Materials 

Radioactive materials (Class 7), meanwhile, are classified according to detailed criteria that fill an entire subpart of the HMR. Considerations for classifying radioactive hazmat include the type of nuclides present (alpha, beta, etc.), the radionuclide number, whether the material is fissile or non-fissile, and more (49 CFR 173 Subpart I).

Watch the video below to find out how the “non-PG” hazard classes and divisions are split up according to degree of danger.