Application of Resuspension Data of Respirable Particles for Early Phase Inhalation Following Deposition Contamination in Radiological Emergencies.

Abstract

Abstract In model experiments, wind resuspension rates, Rr, of respirable particles (<10 μm, aerodynamic diameter) and their time dependence after deposition on representatively contaminated urban surfaces were measured under real-life conditions, taking into account different weather conditions (wind velocities, precipitation) as well as countermeasures (fixation). For contamination by dry deposition of particles, short-term resuspension rates averaged over the first half hour, after exposure to wind with a friction velocity, u*, of 0.8 m s−1 ranged between 0.1% h−1 and 2% h−1 depending on the surface material, whereas after wet deposition, resuspension rates were two orders of magnitude lower. The time pattern of the resuspension rates followed a power law decrease, Rr ∝ t −μ , with values of μ close to 1. The measurements revealed a strong dependence on friction velocity, . For a larger area of 200 × 800 m2 contaminated with 106 Bq m−2 of particles in the respirable size range, applying a simple Gaussian dispersion model airborne activity concentration (Bq m−3) was calculated. On this basis, for an initial time of high windspeed, a cautious resuspension factor of Rf = 5 10−6 m−1 is derived for the first day, which diminishes inversely with time. The exposure of persons to external radiation and to inhaled airborne radioactivity is compared with examples for three radionuclides representing strong beta-, gamma- and alpha-radiation.