Urban dwellers are increasingly vulnerable to failures of technological systems that supply them with goods and services. Extant techniques for the analysis of those technological systems, although valuable, do not adequately quantify particular vulnerabilities. This study explores the significance of weaknesses within technological systems and proposes a metric of “exposure”, which is shown to represent the vulnerability contributed by the technological system to the end-user. The measure thus contributes to the theory and practice of vulnerability reduction. The results suggest specific and general conclusions.