In order to predict the inhalation and dermal exposure during spray application of biocidal products a deterministic model was developed. The model calculates the airborne concentration of the respirable, the thoracic and the inhalable, or any other meaningful size fraction of aerosols containing biocidal substances in indoor environments originating from the release of liquid biocidal sprays. The model is a short term exposure model covering time scales typical for the release process. Long term emissions of vapours from walls and other surfaces are not included. It is assumed that the biocidal product is composed of a non volatile active substance dissolved in a solvent with known volatility. The model is based on a simulation of the motion of released droplets taking into account gravitational settling, turbulent mixing with the surrounding air, and droplet evaporation. The spatial distribution of the concentration is modelled explicitly.

To facilitate the use of the model a programme package was developed that can be executed under WINDOWS 2000. The main input parameters are: the released droplet spectrum, the release rate, the concentration of the active substance, the spatial and temporal pattern of the release process, the vapour pressure of the liquid, the size of the room and the ventilation rate. The path of the sprayer can be explicitly included into the model. For surface treatment by spraying, a droplet deposition module is incorporated in the programme package. This module calculates the fraction of non-impacting droplets which are relevant for human exposure. For room spraying the stopping distance of droplets is also taken into account.