Telecommunication services are essential to modern information systems, especially so for crisis management. Telecoms systems are complex and difficult to analyse. Current risk assessment methods are either not used because of their complexity, or lack rigorous argumentation to justify their results because they are oversimplified. Our challenge has been to develop a risk assessment method that is both usable in practice and delivers understandable arguments to explain and justify its risk evaluations. After experiments to validate the method in laboratory environments, we now present the first results from successful application with practitioners in a regional crisis organization that provides evidence about the practical usability of the...