This work analyses the issue of the acceptable level of risk in the civil protection field from a behavioural perspective. Choosing the acceptable level of risk for a community is a task that political decision-makers are charged with. However, it so happens that politicians do not manage to accomplish this. The reasons for this and some possible solutions have been broached by Di Bucci and Savadori (2018). Starting from that paper, this work aims at proposing some preliminary reasoning on the so-called L'Aquila trial, which involved scientists and Civil Protection officers after the 6 April 2009 Abruzzo earthquake (Italy). Behavioural sciences provide a key to understanding what happened through heuristics and biases that affected all the actors in this story, including the local population, the media, and judiciary, in the frame of coming to no practical decision about the acceptable level of risk. The conclusion is that scientific, technical, and professional communities could and should foster the awareness of people, the media, and political decision-makers (and judiciary), and allow the communities and their decision-makers to take on participated and shared decisions on their acceptable level of risk. These should include the consequences of their decisions and, in a broader perspective, the residual risks that, in a general appraisal, they will decide to accept.