Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 65 studies the combination of various methods of designing for reliability, availability, maintainability and safety, as well as the latest techniques in probability and possibility modelling, mathematical algorithmic modelling, evolutionary algorithmic modelling, symbolic logic modelling, artificial intelligence modelling, and object-oriented computer modelling, in a logically structured approach to determining the integrity of engineering design. . | 624 5 Safety and Risk in Engineering Design in an information integrated technology IIT program considered in Sect. and illustrated in Fig. . The beta factor model is extensively used in predictions in which the appropriate values for beta are selected on the basis of expert engineering judgement. The problem with the model though is the lack of any detailed data for generic systems assemblies and components to provide an adequate assessment of safety in engineering design especially in the preliminary design phase. As a result quite large beta factors have been applied without any justification and caution needs to be exercised when selecting these beta values otherwise the estimates will give unjustifiably pessimistic results with possible over-design of safety-related systems. A somewhat different approach to the beta factor model has thus been taken in which the beta values are not used but predictions are made directly from event data using expert judgment. This approach necessitates identifying the root causes of failure and the likelihood of generating simultaneous failures in similar equipment Hughes 1987 . Fundamentally the basis of this approach typical to IIT is to represent the variability of a component failure probability by distributions that can be estimated directly from a relatively small database. However some researchers have pointed out the deficiencies of expert engineering judgement as applied to common cause failures and contend that analysis of such failures is a knowledgebased decision process and therefore is itself subject to error or uncertainty Do-erre 1987 . b Problems with Applying CCF in Safety and Risk Analysis for Engineering Design Problems with applying CCF in safety and risk analysis for engineering design assessment in the preliminary design phase can thus be reviewed. These problems are summarised as Hanks 1998 The lack of a suitable comprehensive database for CCF. Use of simple CCF models giving pessimistic .
