SIL/LOPA Studies

R B Plant has an experienced team who have carried out numerous studies helping clients to achieve a practical level of risk reduction for new and modified processes across a wide range of sectors.

Our approach is to carry out a Process Hazard Analysis (PHA) using techniques such as HAZOP and ‘What If?’. This will identify the consequence and probability of each hazard and hence a risk matrix ranking. We will then review the PHA to determine which hazards need to be assessed in a separate LOPA study.

As with the PHA, the LOPA sessions are just as structured in which we review layers of protection for each hazard. We work out:

  • Maximum allowable probability for the hazardous event
  • Overall probability of failure for the non-instrumented layers of protection
  • Risk Reduction Factor (RRF) required from the Safety Instrumented System (SIS) โ€“ this will determine the SIL level (Normally 1, 2 or 3).

In most process industries, a SIL rating of more than 2 is normally impractical, with costs and complexities increasing significantly.

Where an SIL rating is calculated to be 2 or higher, this is usually the result of a higher failure probability from the other protective layers. Therefore, we would review and challenge to reduce this failure rate to a figure that results in the SIL rating being 1, or at worst 2, for complex hazards.

This makes the system more intrinsically safe and leaves clients with a cost-effective and easily maintainable SIS.