What is LOPA and SIS?


LOPA - Layer of protection analysis

A semi quantitative tool for analyzing and accessing process safety risks on a process unit
Uses numerical technique to evaluate the adequacy of existing or proposed layers of protection against known hazards
All LOPA starts with a determined consequences to defend against
LOPAs are more Subjective than Objective

LOPA Ratio

-A mathematical factor that defines the amount of a safety gap
-Feeds to the SIS side
-Equal to SIS or SIS amounts
-Higher the TMFL or consequence the larger the ratio and associated SIL to fill.
LOPA process calculation


SIS Process

Safety Instrumented System
-Consist of an engineered set of hardware and software controls that are defined as a critical system and this system will mitigate or stop a determined hazard in a process or unit.
-A SIS is engineered to be independent and to perform specific control function
-SIS is composed of sensors,logic solvers and end devices with connection system between each item.

SIS Process Calculation

SIS process calculation