Effective management of infrastructural networks in the case of a crisis requires a prior analysis of the vulnerability of spatial networks and identification of critical locations where an interdiction would cause damage and disruption. This article presents a mathematical method for modelling the vulnerability risk of network elements which can be used for identification of critical locations in a spatial network. The method combines dual graph modelling with connectivity analysis and topological measures and has been tested on the street network of the Helsinki Metropolitan Area in Finland. Based on the results of this test the vulnerability risk of the network elements was experimentally defined. Further developments are currently under consideration for eventually developing a risk model not only for one but for a group of co-located spatial networks.