On exposure uncertainty quantification from accidental airborne point releases

In any health risk related event such as an air hazardous release, a key question that needs to be addressed is, to what extent an individual is exposed to a hazardous pollutant/agent for a specific time interval at a specific location downstream the release. Any systematic and reliable approach on this problem especially at the application/operation level, requires the knowledge not only of the exposure itself, but also its associated uncertainty quantified using probability density functions. A radically new approach is proposed (a) by making full use of the real detailed inlet flow and release rate signals, (b) by performing a limited number of flow and dispersion simulations in comparison to straightforward approaches, dealing only with steady state and reference inflow and release conditions and (c) by projection of the steady state/reference results to real conditions via appropriate novel scaling approaches based on experimental evidence and theory. A validation exercise has been performed with remarkable results using the well-studied University of Hamburg S2 Michelstadt Wind Tunnel Experiment with building structures representing distinct characteristics of typical central European cities. The message is for an attractive approach that needs further validation with the help of carefully designed experiments combined with dispersion model adjustments and improvements.