Bowtie-based LOPA. For more dynamic risk monitoring!
Hesham Hanafy CFSE, CCPSC, MSaRS, AMIChemE, AMEI, PHA leader
Principal Engineer. Functional Safety Expert.
A Bowtie diagram illustrates the relationships between the hazard, the causes of its realization and its potential consequences. It also includes control and recovery measures in place to prevent the realization of a hazard as well as to mitigate its consequences. However, Bowtie in their own is a qualitative risk analysis technique and mainly focuses on MAHs identified in a previous risk study e.g. HAZID or HAZOP.
On the other hand, LOPA (Layers of Protection Analysis) is a systematic semi-quantitative methodology for examining defense-in-depth and assigning SIL targets for the Safety Instrumented Functions SIFs which can prevent or mitigate certain hazardous scenario. Also, each IPL acts as a barrier to reduce the frequency of the consequence.
The thickness of the arrow represents the frequency of the Consequence if later IPLs are not successful
Bowtie-based LOPA
A bowtie-based LOPA is implementing LOPA calculations on a Bowtie diagram. A bowtie diagram needs to be established for the selected LOPA scenarios, where LOPA terminologies will be reflected on the bowtie as following.?
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After applying the frequencies of the initiating events and Probability of Failure on Demand (PFD) of each barrier/IPL, we will get a quantified bowtie and/or Visualized LOPA.
Bowtie-based LOPAs can also be used for many other technical/process safety applications e.g. to visualize and quantify the risk in case SIL rating of a SIF has been changed (may be based on a new proof test intervals decided) as illustrated in below figure, where the resulted consequence frequency will not be acceptable.
Also, quantified bowtie can be a useful tool in case of overriding a protection layer e.g. overriding a high level alarm. As illustrated below, in case the high level alarm is out of service the frequency of the mitigated consequence will be unacceptable i.e. more frequent than the TMEL of such scenario.
This besides monitoring the risk in case of any change in other factors i.e. duration of batch process, or manning distribution data.
Have you ever tried to have Bowtie-based LOPA for your facility ? Drop me a line if you are interested to know more about the subject!
Suprvisor's Assessor at Rashpetco / Burullus
2 年Valuable information of process safety. thank you.
HSE EPCM Design Loss Prevention Lead Process Safety Assessor, NEBOSH IFC, PSM, SQA9DI, AIMS
2 年Thanks for sharing Hesham this will be live dynamic tool to quantify the SCE safeguard barrier, but as you know LOPA is Single cause Consequence Sceniro based so I think Bowtie Multiple LOPAs tool will be fine. That integrate Risk Quantification with visuals to make clear easy risk based decisions
HSE Consultant, Drilling, Project, Brownfield operation , Process safety, Certified PHA, HAZOP and HAZID Leader, lifting trainer, NEBOSH IGC. NEBOSH Process safety, NEBOSH ID Aand B , Onshore Offshore Rig inspector
2 年Interested?
Technical Safety
2 年Interesting....as a bow tie is one of the most appropriate tool for identification of safety critical elements ...