Layer of Protection Analysis (LOPA) is a tried and tested technique for quickly estimating the likelihood of a given incident occurring.
LOPA makes several simplifying assumptions to speed up the risk assessment process. For example, if two different protective measures are to be taken into account at LOPA, they must be fully independent of both each other and the initiating cause of the incident under consideration.
This means that LOPA is not intended to be fully accurate, but is instead a “semi-quantitative” risk assessment technique.
A LOPA meeting should be chaired by an experienced facilitator who is an expert in the application of the technique. The LOPA also relies on the experience and expertise of a multi-disciplinary team who take part in the LOPA meeting.
LOPA has become the most common method used for “SIL determination” – i.e. the process by which companies decide how reliable their SIFSafety Instrumented Functions need to be to reduce risk to tolerable levels.
As with HazOp, whilst LOPA is part of the “Process Safety” of a particular application, it also fulfils some of the requirements of phase 2 of the Functional Safety Lifecycle; “Allocation of Safety Functions to Protection Layers”. This means that in order to achieve compliance with the functional safety standard, IEC 61511, LOPA must be carried out in such a way that functional safety is achieved. In other words, the LOPA is not an end itself, but is part of a broader approach to both process and functional safety, and this must be recognised in the design and documentation of the LOPA.
In practice, this means that a plan for achieving functional safety should be put in place before HazOp and LOPA are carried out. This plan must also include verification (independent checking) of the LOPA output, and functional safety assessment. =Method’s experience is that taking functional safety into account at the HazOp and LOPA stage makes the subsequent functional safety lifecycle stages far easier to carry out.
=Method can provide expert LOPA facilitators and scribes who will use our tools and templates to deliver a LOPA that is effective, efficient and (as far as is possible) enjoyable. Our approach ensures that the tasks that follow the LOPA (such as Safety Requirements Specification and functional safety assessment) are recognised and supported. =Method can also deliver these follow-on tasks if required.
If you wish to develop your own expertise in this area, =Method has a variety of training courses, such as our IChemE approved Hazard Study Leaders Course. and our Introduction to LOPA course. Following training, we can also offer mentoring to new HazOp and LOPA facilitators as they grow into the role.
E: firstname.lastname@example.org. T: 44 (0)1462 713313. W: www.methodprosafe.com