Dependability Evaluation employs techniques for hardware and software assessment, and derived from these corresponding techniques for the assessment of human reliability. The most prominent shortcoming of such an approach is the lack of a sound psychological basis, and the restriction to operator actions, mostly disregarding organisational and communicational aspects. In this paper the activitytheoretic framework is used as a psychological basis, which allows to model complex systems in such a way that many aspects, which have formerly been studied separately, can be united. The derived method for dependability evaluation can be combined with and complemented by traditional approaches. The theory is illustrated with examples from an industrial case study in the railways sector.