As each atom changes they emit invisible radiation that may cause chemical or biological change-ionising radiation. This can damage the body in some way or other, depending on the type of radiation, and the duration of the exposure.
Ionising radiation is generally dangerous to the human body, depending on the type of radiation, the dose and the duration of the exposure.
Some radioactive materials may also have other hazardous properties, and packages may therefore carry other UN warning signs to indicate subsidiary risks.
Radioactive packages are perfectly safe to handle and transport, because the packaging acts as a shield. They will not create any health hazard for transport workers. However, the rule is to keep any dose of ionising radiation to a minimum. The dose in turn depends on:
- The strength of the radioactive source, the "activity"
- The distance from the source
- The barriers around the source
- The exposure time
The radiation level at the surface must be below 5 m Sv/hour. The packages must be declared as radioactive on the declaration, but they do not need to be labelled. In default of other hazardous properties, they can be carried as ordinary goods.