This paper deals with the first ideas relevant to a knowledge based support for risk engineering when answering tenders or direct customer demands. Indeed, when an offer is defined, it becomes more and more important to analyze the possibilities of: risks occurrence, their consequences and their potential avoidance. Most of the time if it is done, this analysis is conducted manually thanks to a risk expert. In this paper, we propose to assist the expert with a risk engineering aiding tool that relies on a knowledge base and which allows to define and evaluate: (i) the risk and its probability, (ii) the main risk impacts and (iii) the interests of various corrective and preventive actions (impact and probability reductions). We first detail the problem. Then we identify risk knowledge and risk processing. This allows us proposing a knowledge model relevant to the risk engineering entities and some knowledge retrieval queries to support risk engineering.