A SoS is a set of collaborating systems that act towards a common achievement. Risk assessment is important in the early stages of SoS operational development, both for mission objectives and to enable technology which is developed responsibly. The method considers risks that stems from both internal and external interactions which leads to losses for different kind of actors. The method has been applied to a case study of wildfire fighting. The internal interactions are mostly communication between the CSs while external interactions represent dependencies of other systems as well as impacts on other systems. The outcome of the methodology is a network of connected hazards to be used for risk management and for high level SoS requirements.