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The aim of radiation protection standards is to make the radiation workplace as safe as is humanly possible. The gradual evolution over the last 20 years has been towards a more precise definition of the limits for occupational exposure. These have been created not only in terms of short-term effects but also more importantly in terms of long-term risks involving such problems as the potential for carcinogenesis and genetic change. In the United States the National Committee for Radiation Protection has recom­ mended that 5 rems (50 mSv) should remain as the maximum permissible dose equiva­ lent for total body exposure. This would represent the sum of internal and external ex­ posure and should be regarded as the upper limit allowed. The community of radiation users is required to conduct its operations in such a man­ ner that the absolute value of the individual's dose equivalent in rems does not exceed his age in years. There should be additional limits for tissues and organs based on short­ term effects. Therefore, individual organs are limited to dose equivalents low enough to ensure that the dose threshold values are not exceeded.