As an example, pure cobalt-60 has a specific activity of 1,000 curies per gram, which is about one trillion times greater than the definition. However, uranium-238 has a specific activity of only 0.3 microcuries per gram, which is only about 150 times greater than the definition. Although they both exceed the definition of radioactive material in their pure form, either of these materials could be uniformly mixed with enough substance, such as dirt, which would cause the concentration to fall below the definition. Remember, however, that the definition of radioactive material above only applies for transportation. Labels are used to visually indicate the type of hazard and the level of hazard contained in a package.
Labels rely principally on symbols to indicate the hazard.
Radioactive material is the only hazardous material which has three possible labels, depending on the relative radiation levels external to the package. Also, labels for radioactive material are the only ones which require the shipper to write some information on the label. The three labels are commonly called White I, Yellow II, and Yellow III, referring to the color of the label and the roman numeral prominently displayed. A Yellow II must have a TI no greater than 1, and a Yellow III may have a TI greater than 1. Gaseous and liquid radioactive waste, after processing, may be released to the environment.