A Lagrangian particle-tracking model was developed to assess virion passage through compromised membranes. The velocity field created by a hole in the membrane surface is represented by an ideal point sink, superimposed on the uniform flow field through the membrane to describe the flow field resulting from a hole in a flat membrane surface. Catastrophic failure of compromised microfiltration (MF) and ultrafiltration (UF) membranes was observed in laboratory challenge experiments using MS2 and PRD1 phage in 25 mm stirred-cell tests, and predicted by the hydrodynamic model. A "capture cone" defines the extent of hole influence at the membrane surface. A proportion of viruses within the cone passes through the hole. Membrane resistance has the largest effect on the size and extent of influence of this capture cone. For a given membrane increasing transmembrane pressure (IMP) (and flux) decreases the size of the capture cone and lowers the fraction of particle hole passage. Brownian motion is an important factor in diffusive transport of viruses. High resistance, low flux conditions generally increase virus passage through a hole and increase the spread of the capture cone. Virus size has a very small effect on hole passage, an increase in virus size slightly lowers passage. (C) 2011 Elsevier B.V. All rights reserved.