About Performing Layer of Protection Analysis (LOPA)

LOPA can be used to make decisions regarding risk in a hazardous scenario. A scenario is an unplanned event that results in an undesirable consequence. LOPA is usually applied to determine if a scenario is within the risk tolerance criteria or if the risk must be reduced.

When you create a LOPA, you will define the following information:

The risk or initiating event for which you are conducting the LOPA.
The consequence that may occur if that risk is not prevented from proceeding into an undesirable scenario.
The enabling events and conditions that can help in initiating the undesirable event.
The frequency of occurrence of events.
The tolerable frequency of occurrence of event.

Additionally, a LOPA can be linked to the following:

Based on the values that you enter for the fields in LOPA, Conditional Modifiers, and Safeguards, the SIL value is calculated and stored in the Calculated SIL field in the LOPA. A summary of probabilities and frequency values for the LOPA and its associated records appear in the LOPA Summary workspace. Based on the summary, you can evaluate the scenario and make further decision on risk mitigation.

You can create a LOPA, and then link it to the following:

A SIL Assessment for an Instrumented Function in SIS Management.
A Cause-Consequence pair in Hazards Analysis.

If you have linked the LOPA with the SIL Assessment of an Instrumented Function, the SIL value calculated in the LOPA represents the target Safety Integrity Level that the Instrumented Function must achieve (i.e., the amount of risk reduction that the Instrumented Function must provide).

If the LOPA is linked to the Cause-Consequence pair in Hazards Analysis, then the SIL value determines if the safeguards that are currently in place reduce the risk to a tolerable level.