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Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 11

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Handbook of Reliability, Availability, Maintainability and Safety in Engineering Design - Part 11 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. . | 3.2 Theoretical Overview of Reliability and Performance in Engineering Design 83 Table 3.7 Failure mode effect severity classifications Item Classification Description No. 1 Catastrophic The occurrence of failure may result in death or equipment loss A 2 Critical The occurrence of failure may result in severe injury or major system damage leading to loss B 3 Marginal The occurrence of failure may result in minor injury or minor system damage leading to loss C 4 Minor The failure is not serious enough to lead to injury or system damage but it will result in repair or in unscheduled maintenance D Table 3.8 Qualitative failure probability levels Item Probability level Term Description 1 I Frequent High probability of occurrence during the item operational period 2 II Reasonably probable Moderate probability of occurrence during the item operational period 3 III Occasional Occasion probability of occurrence during the item operational period 4 IV Remote Unlikely probability of occurrence during the item operational period 5 V Extremely unlikely Zero chance of occurrence during the item operational period Fig. 3.17 Criticality matrix Dhillon 1999 84 3 Reliability and Performance in Engineering Design Table 3.9 Failure effect probability guideline values Item no. Failure effect description Probability value of F 1 No effect 0 2 Actual loss 1.0 3 Probable loss 0.10 F 1.00 4 Possible loss 0 F 0.10 where Kfm is the failure mode criticality number. 9 the failure mode ratio or the probability that a component will fail in the particular failure mode of interest. More specifically it is the fraction of the component failure rate that can be allocated to the failure mode under consideration. When all failure modes of a component are specified the sum of the allocations equals unity. F the conditional probability that the failure effect results in the indicated severity classification or category given that the failure mode occurs. The values of F are based on an analyst s .