Layer of Protection Analysis and Inherently Safer Processes

Layer of Protection Analysis (LOPA) is an effective way to determine the required Safety Integrity Level (SIL) for Safety Instrumented Systems (SIS) based on the risk of the undesired event. This paper extends the LOPA concepts presented in previous papers to show the effect of inherently safer features. Inherently safer features in aprocess design can reduce the required SIL of the SIS, or can eliminate the need for the SIS, thus reducing cost of installation and maintenance. The discussion includes how to estimate the risk reduction for some inherently safer features. Maintenance requirements and management of change issues for some inherently safer features will be included.