The electrical resistance of a fixed bed of Al2O3 and SnO2, measured during a step change in C3H6 flow through the bed, is reported. The mixed bed was used to simulate a device for simultaneous containment and monitoring of leaks from valves. Simultaneous measurements of the C3H6 concentration breakthrough and the bed resistance showed that Al2O3 was responsible for most of the C3H6 adsorption, whereas low levels of surface adsorption on SnO2 resulted in large changes in the bed electrical resistance. The bed resistance was modelled as a function of the C3H6 breakthrough using first-order kinetics for the reduction of the oxidized SnO2 by C3H6.