1Where the term ‘national authorities’ is used in this Safety Guide, it is intended to apply to all types of regulatory infrastructure, including systems having a single authority or multiple authorities at the national level only and federal systems in which authority is distributed among the relevant regional, provincial or state jurisdictions.

2D values were originally derived in the context of emergency preparedness [23] to establish a reference point corresponding to a ‘dangerous source’ [24, 25] on a scale of the risks that could arise from uncontrolled sources.

3 ‘Risk’ is used here in the broad sense of a multiattribute quantity expressing hazard, danger or chance of harmful or injurious consequences associated with actual or potential exposures. It relates to quantities such as the probability that specific deleterious consequences may arise and the magnitude and character of such consequences. In ranking risks, D values have been used as the normalizing factor as they are based on deterministic health effects — and are therefore applicable for all States. In the interests of international harmonization, no account was taken of the possible cleanup costs following the dispersion of a source, since these will vary from State to State.

4The list of sources given in Appendix I includes examples of sources that have been or were (in 2004) in common use. The list is not exhaustive — there may be sources with higher or lower activities than those described, and the list may also change over time with technological developments.