Abstract: A F-N curve is an intuitive curve for describing the relationship between risk frequency (F) and consequence (N), and it is often combined with the as low as reasonably practicable (ALARP) criterion in determination of the acceptable level of social risks. The previous F-N curve methods suffer from several drawbacks, such as lack of theoretical basis, strong subjectivity, and poor generality for different regions or different risk categories. This paper develops an improved F-N curve through combination with a risk matrix. We integrate the risk criteria into a risk matrix and develop a method of rating the matrix elements by qualitative and quantitative evaluation, and then the risk matrix can be transformed into a F-N curve by using this method. To demonstrate its use, acceptable risk levels of water dams are calculated and compared with those of the traditional method. The results show that the improved F-N curve is more standard and more reasonable and is easy to apply to other types of risks.

Key words: dam risk, risk frequency - consequence curve, risk matrix, acceptable level, criterion