Intro4u2u

What is Layer of Protection Analysis?

LOPA is a semi-quantitative risk analysis technique. It lies in between a HAZOP and a quantitative risk assessment (QRA) in terms of its rigorousness. This technique evaluates risks by orders of magnitude of the selected accident scenarios and builds on the information developed in qualitative hazard evaluation e.g. PHA
LOPA – Diagram
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Layers of Protection
Plants are protected by various layers of protection Examples:

* Pressure Relief Devices
* Flare System
* Fire Suppression System
* Safety Instrumented System (SIS) or Emergency Shutdown System
* Automatic action safety interlock system
* Basic controls, critical alarms
* Community emergency response
* Inherently safe design features
* Operator intervention
* Plant emergency response

When should you use LOPA?

LOPA is applied when a scenario is too complex or the consequence is too severe for the HAZOP team to make a sound judgment based solely upon the qualitative information. On the other hand, it can screen scenarios as a precedent to a QRA.

LOPA helps you to answer the following questions about your facility:

* What’s the likelihood of undesired events / scenarios?
* What’s the risk associated with the scenarios?
* Are there sufficient risk mitigation measures?

Benefits of using LOPA

* Requires less time and resources than for a QRA but is more rigorous than HAZOP.
* Many process safety systems are over-engineered for safety with additional costs and have unnecessary complexity. LOPA helps focus the resources on the most critical safety systems.
* Acts as a decision making tool, helps make judgments quicker, resolves conflicts and provides a common base for discussing risks of a scenario.
* Removes subjectivity while providing clarity and consistency to risk assessment.
* Improves scenario identification by pairing of the cause and consequence from PHA studies.
* Helps to compare risks based on a common ground if it is used throughout a plant.
* Helps decide if the risk is As Low As Reasonably Possible (ALARP) for compliance to regulatory requirements or standards.
* Identifies operations, practices, systems and processes that do not have adequate safeguards.
* Provides basis for specification of IPLs as per ANSI/ISA S84.01, IEC 61508 and IEC 61511.
* Helps to decide which safeguards to focus on during operation, maintenance and related training.
* Support compliance with process safety regulations – including OSHA PSM 1910.119, Seveso II regulations, ANSI/ISA S84.01, IEC 61508 and IEC 61511.