Packing Groups (PG I, II, III) & Precedence of Hazards Matrix

Packing Groups (PG I, II, III) & Precedence of Hazards Matrix

When classifying dangerous goods for air transport, assigning the correct hazard class is only the first step. Shippers must also determine the Packing Group (PG) to indicate the relative degree of danger and use the Precedence of Hazards Table (Table 3.10.A) whenever a chemical substance, mixture, or solution possesses multiple hazardous properties.

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Fundamentals of Packing Groups (PG I, PG II, PG III)

Dangerous goods are assigned to Packing Groups according to the degree of danger they present:

• Packing Group I (PG I): High Danger (requires the most robust, stringently tested UN specification packaging).
• Packing Group II (PG II): Medium Danger.
• Packing Group III (PG III): Low Danger (minor danger).

                                  PACKING GROUP HIERARCHY
  ┌─────────────────────────────────┬─────────────────────────────────┬─────────────────────────────────┐
  │     PACKING GROUP I (PG I)      │     PACKING GROUP II (PG II)    │    PACKING GROUP III (PG III)   │
  ├─────────────────────────────────┼─────────────────────────────────┼─────────────────────────────────┤
  │ HIGH DANGER                     │ MEDIUM DANGER                   │ LOW DANGER                      │
  │ Tested for 1.8 m drop test      │ Tested for 1.2 m drop test      │ Tested for 0.8 m drop test      │
  │ Packaging symbol: 'X'           │ Packaging symbol: 'Y' or 'X'    │ Packaging symbol: 'Z', 'Y', 'X' │
  └─────────────────────────────────┴─────────────────────────────────┴─────────────────────────────────┘

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Classes and Divisions Without Packing Groups

It is a fundamental rule of IATA DGR classification that not all hazard classes use Packing Groups. The following classes and sub-divisions use specialized classification criteria instead of Packing Groups:

• Class 1 (Explosives): Classified by Division (1.1–1.6) and Compatibility Group (A–S).
• Class 2 (Gases): Classified by Division (2.1, 2.2, 2.3) and cylinder pressure/refrigeration specs.
• Division 5.2 (Organic Peroxides): Classified by Type (Types A through G).
• Division 6.2 (Infectious Substances): Classified by Category A (UN 2814/2900) or Category B (UN 3373).
• Class 7 (Radioactive Material): Classified by Package Type (Excepted, Type A, B, C) and Category Label (I-WHITE, II-YELLOW, III-YELLOW).
• Class 9 (Certain items): Standalone lithium batteries and magnetized materials do not use Packing Groups.

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Multi-Hazard Substances & Absolute Precedence Rules

When a substance, mixture, or solution possesses characteristics corresponding to two or more hazard classes, a systematic determination must be performed to identify:

1. The Primary Hazard Class (dictates primary packaging instruction, label, and Shipper's Declaration entry);
2. The Subsidiary Risk(s) (dictates secondary hazard labels and stowage segregation);
3. The Overall Packing Group.

Absolute Primary Precedence Rules (Overrides)

Under IATA DGR Section 3.10, certain hazards ALWAYS take absolute precedence over any other hazard, regardless of concentration or secondary parameters:

1. Class 7 Radioactive Material (in forms other than excepted packages);
2. Class 1 Explosives;
3. Class 2 Gases;
4. Desensitized explosives of Class 3 and Division 4.1;
5. Division 4.1 Self-reactive substances;
6. Division 4.2 Pyrophoric substances;
7. Division 5.2 Organic Peroxides;
8. Division 6.1 Packing Group I Inhalation Toxicity substances ($V \ge 10 \times LC_{50}$ and $LC_{50} \le 1000\text{ mL/m}^3$);
9. Division 6.2 Infectious Substances.

Everything outside that list — Class 3, Divisions 4.3 and 5.1, the remaining Division 6.1 entries, Class 8 and Class 9 — is resolved through the Table 3.10.A matrix below.

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Application of IATA Table 3.10.A (Precedence of Hazards Table)

For multi-hazard substances not covered by absolute precedence overrides, shippers must consult Table 3.10.A (Precedence of Hazards Table). The matrix intersects the competing classes/divisions and their respective packing groups. The extract below shows how the table reads — always resolve a live classification against the printed Table 3.10.A in the current edition rather than against a summary:

Step-by-Step Practical Examples

Example 1: Liquid Mixture with Flammability & Oral Toxicity

• Properties: Flash point $15^\circ\text{C}$, Initial boiling point $50^\circ\text{C} \rightarrow$ Class 3, PG II.
• Toxicity: Acute oral $LD_{50} = 25\text{ mg/kg} \rightarrow$ Division 6.1, PG II (Oral).
• Table 3.10.A Lookup: Intersect Class 3 PG II and Division 6.1 PG II (Oral).
• Result: Primary Hazard = Class 3, PG II; Subsidiary Risk = Division 6.1.
• Proper Shipping Name: Flammable liquid, toxic, n.o.s. (UN 1992).

Example 2: Liquid Mixture with Flammability & High Skin Corrosivity

• Properties: Flash point $45^\circ\text{C}$, Initial boiling point $110^\circ\text{C} \rightarrow$ Class 3, PG III.
• Corrosivity: Full thickness skin destruction at 2 minutes exposure $\rightarrow$ Class 8, PG I.
• Table 3.10.A Lookup: Intersect Class 3 PG III and Class 8 PG I.
• Result: Primary Hazard = Class 8, PG I; Subsidiary Risk = Class 3.
• Proper Shipping Name: Corrosive liquid, flammable, n.o.s. (UN 2920).