Footnote 56
Examples of giving priority to reducing activity concentrations of 222Rn in those situations for which such action is likely to be most effective include (i) specifying the levels of activity concentrations of 222Rn in dwellings and other buildings with high occupancy factors at which protection can be considered optimized; (ii) identifying radon prone areas; (iii) identifying characteristics of buildings that are likely to give rise to elevated activity concentrations of 222Rn; and (iv) identifying and requiring preventive measures for radon in future buildings that can be introduced at relatively low cost.