The safe community is now at time of globalisation very dependent on a safety level of critical infrastructure ensuring the territory by basic services necessary for humans´ live as there are energy, water, food, information etc. Series of events from recent years connected with critical infrastructure failures showed its high importance. The critical infrastructures represent multistage mutually overlapping systems, i.e. big complex systems, the type of which is a systems system. The paper presents the model for critical infrastructure safety management based on this reality and it shows the way how simply to determine the criticality of individual infrastructures and the whole critical infrastructure.