Application of Layer of Protection Analysis (LOPA) in Verification of Safety Integrity Level of Instrumented System

Incomplete process hazard analysis (PHA) and poor knowledge management have
been two major reasons that have caused numerous lamentable disasters in the
chemical process industry. To improve the safety integrity of a process system, all
risk should be reduced to a tolerable limit. One way of doing it is by adding layers of
protection which include inherent safer design, basic process control system (BPCS),
alarms, SIS, physical protection, and emergency response procedure. These layers
however, are cost to the process industry in term of implementing it as well as
maintaining the quality of the layers. Therefore, understanding the required safety
integrity level (SIL) of a process is essential in order to meet the tolerable risk target
as well as to optimise the cost of a safety system. Meanwhile, layer of protection
analysis (LOPA) is a simplified approach to verify SIL of a process system.
Nevertheless, the method is relatively new and various modifications have take place
by different entities. Therefore, there is a need to maintain the consistency of the
LOPA result by adhering to a standard procedure and practise as well as clear
direction provided by Centre of Chemical Process Safety (CCPS). This can be done
easier by developing a framework for LOPA analyst to follows as well as tailored to
the company background and history.