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Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 68

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Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 68 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. . | 654 5 Safety and Risk in Engineering Design The actual degree of safety incidents This is evaluated according to the contribution of the actual physical condition of the equipment to its safety the actual downtime frequency as well as the actual reportable incident frequency arising from the functional failure history of the equipment resulting in an asset loss consequence of failure. Besides safety operational and physical consequences of failure the other consequences economic environmental systems and maintenance are typically measured as the cost of losses plus the cost of repair to the failed item and to any consequential damage although in reality all safety consequences are eventually also measured as a cost risk . These cost risks of failure are also defined as the result of multiplying the consequence of failure i.e. the cost of losses plus the cost of repair by the probability of its occurrence. Reliability analysis in engineering design tends however to simplify these risks to the point of impracticality where for example consideration is given only to single modes of failure or only to random failure occurrences or to maintenance that results in complete renewal and as new conditions. In reality the situation is much more complicated with interacting multiple failure modes variable failure rates as well as maintenance-induced failures that influence the rates of deterioration and subsequent failure Woodhouse 1999 . It is somewhat unrealistic to assume a specific failure rate of equipment within a complex integration of systems with complex failure processes. At best the intrinsic failure characteristics of components of equipment are determined from quantitative probability distributions of failure data obtained in a somewhat clinical environment under certain operating conditions. The true failure process however is subject to many other factors including premature or delayed preventive maintenance activities conducted during shutdowns of process .