Many ventilating systems do not function properly due to the fouling of ducts and components, There is a need to study a wide range of different duct systems, in order to reduce the deposition I ate in absolute terms, thus arriving at a more efficient system. A preliminary study is conducted in the laboratory to determine the flow behaviour of aerosol particles in relation to the airflow for ducts of various aspect ratios. A constant-injection tracer-gas technique is used to determine the airflow rate in the ductwork. SF6 tracer gas and smoke particles were injected at a constant rate into the inlet of each duct and their tracer-gas concentrations in ppm and smoke-particle concentration in mg m(-3) were monitored at various points downstream. Algorithms were established for the deposition rate of smoke particles in various ducts, The results showed that the deposition rate of smoke particles was strongly influenced by the airflow rate and size of the duct.