The CLEANAIRNET research project* has been launched in 2008 with a funding of the French National Research Agency (ANR). It is dedicated to the study of air flows in the ventilation networks of food factories together with the mechanisms of deposition and re-suspension of bio-aerosols in the ducts, first through an in-situ analysis in industrial sites and then through experiments carried out on experimental benches. In a second step, the design of innovative principles of particle trapping will be proposed, leading to the development of controlled fouling up zones allowing a safer and better controlled operation of the ventilation networks. We present the main results of the first half of the project. Physical and microbiological measurements have been carried out on four industrial sites. A wide range of air flow conditions have been characterized. A detailed description of aerosol load and particle sizes is now available. Samples from the inner duct surfaces and aerosols have been collected and submitted to microbiological analysis. The monitoring of these data along a six months period in each site enables an analysis of the influence of the network structure, the food production operations and the working sequences on the nature and quantities of bioaerosols. The evolution of surface contamination has also been monitored, leading to original information on the stabilized level rapidly reached. Using the in situ information on the dominant particle sizes and the network characteristics, an improvement of the aerosol deposition models will be obtained through an experimental approach involving works on scaled-down and real-scale test setups.