  We study the time until a filter becomes clogged due to the trapping of
suspended particles as they pass through a porous medium. This trapping
progressively impedes and eventually stops the flow of the carrier fluid. We
develop a simple description for the pore geometry and the motion of the
suspended particles which, together with extreme-value statistics, predicts
that the distribution of times until a filter clogs has a power-law long-time
tail, with an infinite mean clogging time. These results and its consequences
are in accord with simulations on a square lattice porous network.
