(57a) Does Your SIS System Still Comply with Yout LOPA and SRS?

It is often assumed that a SIS system forever meets all the SIS requirements of the project Layers of Protection Analysis (LOPA) and Safety System Requirements (SRS). In reviewing a number of installed refinery SIS systems with respect to maintenance issues and operational issues a pattern starts to emerge regarding SIS perception, SIS design and SIS equipment selection. Those involved in LOPA and SRS often assume a theoretical or ideal SIS environment which often doesn't reflect reality. Refinery sulphur train Burner Management Systems (BMS) often have the most SIS issues but operationally are required to be the most reliable SIS systems. This conflict manifest itself in having too many SIS field devices in bypass mode. LOPA and SRS teams need to consider specific SIS equipment reliability rather than to use generic failure rate or calculated failure rate numbers.