The above deals with the classification but, in addition, certain classes have packaging/danger groups that determine any specific packaging requirements.

Note UN recommendations only categorise them, they do not actually define the package. For this reason packing requirements are not the same for transport by Air, Sea, Road and rail.

Road and rail requirements vary within geographical area.

This means additional or different packing and labelling requirements for differing modes of transport.

COMPATIBILITY TABLES. - In addition to the ability to identify the inherent hazard of the substance, this classification serves the purpose of an indicator to the compatibility of the substances and in warehouses or in holds especially in the case of spillage. In this way hazardous substances can be properly segregated and properly placed so as to avoid any cross-reactions and provide proper safeguards.
There are limitations in the case of storage, for example, "Dangerous When Wet" items are better isolated from flammables especially if water is the possible mitigating agent.