Revision of the Skin Dose Limit

The Nuclear Regulatory Commission (NRC) is amending its regulations in 10 CFR part 20 to change the definition and method of calculating Shallow-dose equivalents (SDEs) by specifying that the assigned SDE must be the dose averaged over the 10 square centimeters of skin receiving the highest exposure, rather than 1 square centimeter as stated in the existing regulation. A result of this rulemaking is to make the skin dose limit less restrictive when small areas of skin are irradiated (i.e. more representative of actual health risks) and to address skin and extremity doses from all source geometries under a single limit. This change requires measuring or calculating SDEs from discrete radioactive particles (DRPs) on or off the skin, from very small areas (1.0 square centimeter) of skin contamination, and from any other source of SDE by averaging the measured or calculated dose over the most highly exposed, contiguous 10 square centimeters for comparison to the skin dose limit of 50 rem (0.5 Sv). The Commission believes that although the less restrictive limit on dose to small areas of the skin might permit more frequent, transient, observable effects such as reddening of the skin, the change nevertheless represents a substantial increase in worker protection because reduced monitoring for DRPs will result in reduced external dose and reduced use of protective clothing will result in fewer industrial hazards in the workplace.