Hazards Australasia 2018
LOPA has become the go-to method for establishing the reliability requirements of safety instrumented functions (SIFs). However, the objectives of a LOPA study are not realized if the reliability requirements are not actually achieved and/or maintained throughout the life of the SIF. In fact, the LOPA study is just one of several essential steps in the Functional Safety Lifecycle, as defined in 61511. Every step in the lifecycle must be fully implemented to ensure that SIFs provide adequate protection.
This paper highlights some of the common pitfalls and omissions in implementing the Functional Safety Lifecycle. It focuses on the relationship between LOPA and other functional safety activities, including SIL verification (reliability analysis), operation, maintenance and modifications. The paper suggests possible solutions to some important questions in functional safety, such as:
- Are the assumptions made during the LOPA workshop accurately reflected in data from the field?
- How can we ensure that the component failure rate data, used to analyse SIF reliability, are accurate and appropriate for the SIF’s environment and duty?
- How does the plant’s maintenance regime affect SIF reliability?
- What are the implications of SIF modifications on the reliability of the SIF?
- How long is the SIF’s operational life in practice? If it still seems to work, can the SIF be used beyond its design life?
- What consideration should be given to the operation of non-SIF protection layers?