Why worry about something that isn't going to happen
June 10, 2019
May 23, 2015
Has anyone conducted LOPA analysis with Upper & Lower values on the Frequency & Probability values ?
We all know that the best data is site specific, however it's not always available and therefore we often use published sources such as Exida SERH, SINTEF OREDA, CCPS PERD etc.
Not knowing exactly how comparable our 'actual' data is or will be against the generic values; applying upper & lower "confidence" values provides an overall range of outcomes around a medium (generic published) basis.
Obviously as you multiply up the probabilities, the range gets bigger (ref attached example image) which gives the designer a challenge in determining which frequency result to compare to the risk tolerability criteria.
I've seen this approach applied to SIL Verification calculations to provide a range of possible PFDavg, but not aware of it being used for SIL Determination (LOPA).