Crisis response authorities have to deal with the unpredictability of their population's behavior. One of the complex challenges is to understand the people's reaction after an official alert in a crisis situation has been issued. This paper elaborates a knowledge base to describe impacting factors on human reactions in alerting situations. For this purpose, a literature review in the theme of human behavior after warnings was conducted and augmented with information gathered in a series of interviews in German-speaking countries. The outcome is phrased as factors that might impact the human reaction to a warning. This knowledge base shall support crisis management practitioners in the elaboration of alerting strategies as well as allow researchers to systematically structure human behavior aspects for the purpose of modeling and simulating alert effects.