Which hazard class uses a transport index for loading limits?

The correct choice is related to Class 7, which pertains to radioactive materials. This class is unique in that it employs a transport index to indicate the degree of hazard presented during transportation. The transport index is a numerical value that reflects the degree of radiation exposure risk associated with the package and is intended to help ensure safe loading and transport.

For radioactive materials, the transport index is essential for determining how much radiation is present and how far packages of this class can be separated from one another during transport for safety purposes. It aids in planning the stowage and loading of these materials in accordance with regulatory requirements to minimize exposure to personnel and the environment.

In contrast, the other hazard classes do not utilize a transport index in the same way. Class 2 (gases) primarily focuses on the physical and chemical properties of gases without the need for such an index. Class 6 (toxic substances) and Class 4 (flammable solids) each have their own labeling and handling requirements based on different criteria, but they do not rely on a transport index for loading limits like radioactive materials do.