The CCPS book clearly states LOPA uses a single cause-consequence pair, the worst combination, for the order-of-magnitude risk estimate. Other methods, especially Fault Tree, are more appropriate to treat multiple initiating events. Many times simply summing the initiating events is not appropriate due to limitations in the simplifying assumptions behind the development of LOPA. There [...]
There is a lot of discussion elsewhere on ALARP (and/or ALARA). However, a company can add too many protection layers and invite shortcuts of one or more of the IPLs over the long-term, since staff are pretty sharp at figuring out when the "plumbing is over-tinked". We advise folks to reach barely tolerable on each [...]
I like LOPA as well as the next person; I'm one of the two co-originators as you likely know. But all of the quantitative methods use "statistical" values (but not as statistical as most think) that have in fact been "voted" upon by "experts", so you can either let LOPA or QRA analyst use factors [...]
The main benefit to a business (set aside any "government regulator" issues for now, since that should not be very important) in implementing SIS standards is the consistency in understanding the safeguard level for an instrumented safety system. But, there are disadvantages to following "only" IEC 61508/61511. One disadvantage is that the PFDavg calculated for [...]
Since I'm one of the two originators of LOPA in 1995 and one of the two primary authors of the CCPS books on LOPA (2001 and 2012), I (and many others) believe we are doing Too Many analysis. A well-structured and well led PHA team does 95% of the risk analysis and 99% of the [...]
