(22a) HAZOP, LOPA, SIL: Be Careful What You Ask for!

In recent years Process Safety Engineers have promoted the use of HAZOP to identify hazards and assess safeguards, followed by LOPA to identify if additional protection layers are necessary and, if they are to be provided using safety instrumented functions, how reliable the SIFs need to be. Finally SIL verification (reliability analysis) is used to show that the selected SIF sensors, logic and final elements will achieve the required reliability performance for the selected testing regime.

Given that the addition of instrumented protection systems to a facility design is often viewed by engineering contractors and operating companies as easier to implement than changes to the overall process design, it has led to a proliferation of Safety Instrumented Functions/Safety Instrumented Systems (SIF/SIS), the implications of which industry has yet to fully understand. This paper will discuss some of these implications and makes a number of observations regarding approaches to improve the integrity of process plants.