Analysis of potential radiobiological effects related to a unified skin dose limit

A unified skin dose limit of 0.5 Sv at a depth of 70 microm averaged over the highest 10 cm2 of skin exposed was evaluated to replace the existing limit of 0.5 Sv averaged over 1 cm2. This limit would apply to all exposures including non-uniform exposures such as from hot particles on or off skin, skin contamination, or beams of charged particles or photons. The probabilities and severity of both stochastic and deterministic risks were estimated for a wide range of worst-case exposure scenarios using published radiobiological data and calculations of radial- and depth-dose distributions. Results indicate that exposures at the unified dose limit have the potential to cause effective doses of about 17 microSv (1.7 mrem), estimated stochastic risks of <3.3 x 10(-7) fatal skin cancers, and <1.6 x 10(-4) non-fatal skin cancers. The worst deterministic effects were estimated to be (a) based on a 2 Gy threshold, transient erythema induction to an area of 2.5 cm2 for uniform skin contamination over this same area and 0.65 cm2 for a 60Co hot particle 3 mm off of skin, (b) based on data for pig skin, 50% probability that 0.5 cm2 of skin would suffer 20% dermal thinning for uniform contamination with 106Rh spread over the same area, and (c) 10% probability of barely detectable transient acute necrosis or ulceration for 60Co or activated fuel particles 0.4 mm off of skin. It was concluded that the unified limit would provide a more logical system of dose control with possible savings of whole-body dose and other benefits.