Upcoming service
LOPA & SIL
As a natural continuation of our work with risk analysis and HAZOP, PSL AB is currently building up an offering in LOPA and SIL classification – two established methods that take risk management further, from identified deviations to verified, correctly sized protection.
A HAZOP identifies what can go wrong; LOPA and SIL answer the next question: are the safeguards already in place sufficient, and how reliable must a new safeguard be for the risk to be considered acceptable?
Why it is needed
- Correctly sized protection – avoids both oversized safety systems and undersized solutions that leave a residual risk
- An established method at high-risk plants – a recognized way of showing that the risk has been sufficiently reduced, especially at Seveso establishments and where safety instrumented systems (SIS) are used as protection layers
- Part of the IEC 61511 workflow – the standard's functional safety lifecycle requires the necessary risk reduction to be determined and the protection layers to be verified; LOPA is one of the methods the standard describes
- May be asked for by insurers and third-party reviewers as part of the basis for a risk assessment of the plant
What the service is
LOPA (Layer of Protection Analysis) is a semi-quantitative risk analysis method developed by CCPS and described in the standard IEC 61511, del 3, bilaga F (part 3, annex F). The method builds on the scenarios identified in a HAZOP and evaluates each independent protection layer (IPL) in the chain between a cause and a serious consequence.
SIL (Safety Integrity Level) states how reliable a safety instrumented function (SIF) in a safety instrumented system (SIS) must be. The concept is defined in IEC 61508 and IEC 61511 and is expressed in four levels, SIL 1 to SIL 4, where each step corresponds to a tenfold increase in risk reduction. The SIL requirement is often determined with LOPA, but other methods, such as a risk graph, are also used.
Please note: LOPA and SIL classification are not currently part of PSL AB's regular, established range of services. This section describes a service under development and the role these methods play in a complete risk management process.