@onsidering such benefits, exposure at .the level of the RPG is considered as an acceptable risk for a lifetime. The RPG's are expressed in terms of annual exposureTenvironmental monitoring is a necessary part of complying with the RPG guidance, the intensity and frequency of measurements being determined by requirements to be able to detect sharply rising trendsand to provide prompt and reliable information on the effectiveness of control actions, Source control actions and monitoring efforts are to increase as predicted exposures move through a range of values and approach the numerical value of the RPG. A sharply rising trend approaching the PRG would suggest strong and prompt action. The magnitude of the action should be related to the degree of Likeldhood that the RPG would be exceeded. a % The child, infant, and unborn infant are identified as being more sensitive to radiation than the adult. Exposures to be compared with the guidance are to be derived for the most sensitive members in the population. The guide for the individual applies when individual exposures are known, otherwise, the guide for a suitable sample (one-third the guide for the individual) is to be used. This is an operational technique and may be modified to meet special situations. The FRC primary numerical guides, expressed in rem, are provided These in two reports, FRC Nos. 1 and 2, land!are summarized in Table I. Through calculational methods using dose models, secondary numerical guides have been developed by FRC and are expressed in terms of daily intake