LOPA Layer of Protection Analysis

According to the IEC 61508 / 61511 standards a risk analysis has to be performed for Loss Of Containment scenarios from a HAZOP study which are considered potentially dangerous. The method for this analysis is free to choose. Some companies use a risk matrix, some a risk graph and others the method LOPA (Layer of Protection Analysis). Each method has its pros and cons.

In order to determine the risks in objective way, some factors are important:

  • Performance by a team of experts (eg HAZOP team) through a brainstorming session.
  • An experienced chairman who knows well the risk method, knows how risks can be reduced, and will maintain a balance between brainstorming and make progress.

Schematic view of LOPA.

It is essential to document the risk assessment (SIL classification) properly, the choice of the various parameters must be clear and explained in detail.

Using LOPA, it is essential to know which incident frequences the company tolerates. What is the risk reduction of independent protection layers and frequency modifiers?

A pitfall is to think too optimistic about certain risk reduction. For example, the risk reduction of an alarm.

The LOPA methodology is based on the LOPA standards of CCPS.

CCPS books about LOPA