LOPA Overview

A typical chemical process has various Layers of Protection (LOP). These can be the process design itself, the Basic Process Control System (BPCS), operator intervention, the Safety Instrumented Systems (SIS), active protection (such as relief valves), passive protection (such as dikes and blast walls), etc. Layers of Protection (LOP).

These should be Independent Protection Layers (IPLs) that serve to either prevent an Initiating Event (e.g., loss of cooling) from developing into an incident (e.g., a release of a dangerous substance), or to mitigate the consequences of an incident once it occurs.

A Layer of Protection Analysis (LOPA) is a risk management technique to provide a detailed, semi-quantitative risk assessment. The Consequence of the Hazard Scenario, the Initiating Event’s Frequency, and the likelihood of failure of the layers of protection, are all assessed, to approximate the risk. The primary purpose is to assess the adequacy of the existing or proposed layers of protection against a Hazard Scenario.

Typically, when a high-Consequence scenario, usually involving a combination of equipment and human failures, is identified during a Hazard and Operability study (HAZOP), a LOPA is initiated for a closer, more careful assessment of this Hazard Scenario.