High-velocity jets of water or solvent are commonly used to clean tanks which have contained flammable liquids. This process creates a charged mist which can lead to the generation of an electrostatic spark or brush discharge that may ignite any flammable atmosphere present. Operators need to know the risk associated with their processes and modelling can help assess it. Numerical techniques are available to solve electrostatic problems for general tank geometries but tend to be expensive and difficult to use. This paper shows how Green's function can be used to solve Poisson's equation fur a vessel of cylindrical geometry and finite length containing charged mist. For uniform space-charge density, an analytical solution can readily be implemented using cheaper proprietary software. An example from an industrial investigation is described in which the internal walls of a cylindrical vessel were washed with solvent jets. (C) 2001 The Institute of Physics. Published by Elsevier Science Ltd. All rights reserved.