Yeh and Hsieh (2007) proposed a FMEA based on fuzzy theory approach and developed a prototype of the risk assessment experts system. They presented the analysis of a sewage treatment system (STS) to demonstrate the proposed fuzzy FMEA method. They concluded that the application of linguistic terms allows experts to provide a more reasonable and meaningful information for these three parameters. Fuzzy rule base could allow experts to construct the more realistic and logical rules.