Specifying task models of socio-technical systems is especially relevant when safety-critical processes andsystems are concerned. It has been found that communication in safety-critical socio-technical systems is a major root forcritical incidents and accidents. In a recent project we created a task modelling environment taking into account the specialneeds for this type of systems. The model allows the specification of risk assessment factors, barriers and the informationflow between tasks. In this paper we present the approach with special emphasis on the specification of communicationwithin the model. We show how communication can be made an explicit concept necessary for the successful execution ofco-operative tasks and discuss the integration of communication into the framework of task decomposition.