Quantitative Risk Assessment is a powerful tool for evaluating the risk of industrial facilities and land use planning. Its use in Engineering Design requires a criterion to define the wellness of different designs. Current criteria are exhaustive and require big efforts to be applied. In the present work it is demonstrated that a simple criterion based on the surface enclosed in isorisk curves is useful for comparing the results of different QRA. Using such criterion, some existing radiation and overpressure threshold values producing domino effect in pressure tanks are compared. The Probit equations are used to model the domino effect. The method of surfaces enclosed in isorisk curves gives coherent results evaluating the risk associated to different layouts of a plant, opening the door of using QRA in the design of industrial facilitie