Occluded cell corrosion is a major contributor to unexpected and premature failures. A reliable, on-line instrument to monitor for occluded cell corrosion would generate benefits of a decreased frequency of failures and a more reliable estimation of service life. This paper reviews the thermodynamic and kinetic bases for such a practical monitor to show that the concept is sound. Crevice dimensions, cathode-to-anode area ratio, and defined hydrodynamics—parameters important in the in-plant monitor—are defined in this discussion. Finally, a conceptual model of a proposed in-plant monitor is presented. The dimensions and geometry are derived from the discussion of the theory.