Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 57 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. . | 544 5 Safety and Risk in Engineering Design Fig. Cause-consequence diagram man et al. 1994 and programmable user modelling applications Blandford et al. 1999 have emerged to reconcile deficiencies in the tree-based analysis techniques. Furthermore although the use of techniques are adequately suitable in designing for safety of process engineering designs their use in designing for systems control is complicated by the large number of ways that computational control can address or even contribute to hazardous system states. This problem is solved by the use of a relatively new forward analysis technique called deviation analysis Leveson 1995 . Deviation analysis DA is based on the underlying assumption that many accidents or incidents are the result of deviations in system variables where a deviation is the difference between the actual and correct values appropriate for system control. The method originates from the forward analysis technique of software deviation analysis SDA in which hazardous behaviour in system control software is analysed. DA is an extension of the technique to system control hardware. Deviation analysis determines whether hazardous systems behaviour can result from a class of input deviations inclusive in the broad range of process characteristics such as capacity input throughput output and quality. It is a means of determining system component robustness or in safety terminology its survivability or how it will behave in an imperfect environment. Hazardous operability studies HAZOP short for hazard and operability was first introduced by engineers from ICI Chemicals in the UK in the 1970s. The method entails the investigation of deviations from the design intent for a process engineering installation by a design team with expertise in different areas such as engineering operations maintenance safety and chemistry. The team is guided in a structured process by using a set of guidewords to examine deviations from normal process .
