How are the packing group classifications defined within the IMDG Code?

Packing group classifications within the IMDG Code are used to indicate the degree of danger presented by hazardous substances, influencing the type of packaging required for safe transport. There are three packing groups: Packing Group I, which indicates substances presenting a high danger; Packing Group II, indicating substances presenting a medium danger; and Packing Group III, indicating substances presenting a low danger. The criteria for assigning a substance to a particular packing group depend on the specific hazard class and are based on factors such as oral toxicity, dermal toxicity, inhalation toxicity, corrosivity, and flammability. For example, for toxic substances, the packing group is determined based on the LD50 (lethal dose, 50%) values for oral and dermal exposure, and the LC50 (lethal concentration, 50%) value for inhalation exposure. Substances with lower LD50/LC50 values, meaning they are toxic at lower doses/concentrations, are assigned to a higher packing group (I or II), requiring more robust packaging. Similarly, for corrosive substances, the packing group is determined based on the rate and extent of corrosion to steel or aluminum. Substances that cause rapid and severe corrosion are assigned to Packing Group I. The packing group assignment dictates the type of packaging that must be used, including the materials, construction, and testing requirements. Substances in Packing Group I require the most stringent packaging to withstand severe handling and transport conditions, while substances in Packing Group III require less robust packaging. The packing group is a critical element of the shipping documentation and package labeling, informing handlers of the relative hazard posed by the substance and the necessary precautions.