Formal Safety Assessment (FSA) considered at IMO, is formal methodology for improving the transparency and accountability of decision related to amendment to the regulations. FSA consists of PSA (Probabilistic Safety Assessment) and cost and benefit assessment. Risk assessment is the most important and difficult part to realize FSA. This paper introduces a methodology for risk assessment and a system for risk assessment composed of several programs including disaster development simulation and evacuation simulation. Furthermore, the result of the trial application of the system, in which the effect of sprinkler systems, i.e., one of the Risk Control Options (RCOs), on the risk due to cabin fire is estimated. Though there are many defects and problems in the system and the methodology at present, i.e., discussed in this paper, the methodology is considered to contribute for reducing the arbitrariness at the decision related to rule making process.