This is one of questions asked by a abaper in SDN, I thought of posting this here for everyone's convenience
Specification is a description that uses identifiers, value assignment types and header information showing the physical chemical properties, dangerous goods classifications, medical data, who created and when created, and also NAM, NUM, FRM identifiers so that you can retrieve them during search. In EHS there are different types of Specifications - based on the type of information you enter for each of them. It could be Substance Specification, Agents Specifications, Packaging Specification or even Dangerous Goods Classification specifications.
In order to create all these substances there is one workbench called Specification Workbench. Coming to the option of Transaction Code CG02, in EHS though specification workbench is a common area for creating a Specification, If you creating different specification types (Substance, Agents, Dangerous Goods classification, Waste Codes) you can directly access those selected workbench using dedicated T codes. Like CG02BD for accessing all the specification workbench, CG02 for Substances workbench, CBIH92 for Accessing Agents Specification like that.
Hypothetically assume that you have different material types if you want to choose one material type you have an option of selecting one T CODE and for another Material type choosing another TCode. similar concept applies here.