LOPAS (Layer Of Protection Analysis Software)

Layer Of Protection Analysis (LOPA) is a technique used for analysing and assessing risk through semi-quantitative methods. Oil gas and petrochemical facilities typically use various protection layers to lessen the likelihood of a hazardous consequence. These have included process design, Basic Process Control Systems (BPCS), Safety Instrumented Systems (SIS), passive devices e.g. dikes and blast walls, active devices such as relief valves and human intervention. Decisions over how to implement these have often been subjective and down to the individual perceptions. The methodology can be used to help organisations demonstrate that risks are As Low As Reasonably Practicable (ALARP), which is often a regulatory requirement.

LOPA is a risk based approach that analyses individual protection layers for their effectiveness. Predetermined risk criteria are then used for comparison with the combined effects of risk assessment. The following are example applications of the methodology and software:

  • Can be used at any point during the life cycle of a process or facility.
  • Examine scenarios identified in HAZOP, HAZID etc. classifying and assisting in the selection of the best protection methods.
  • Aids risk assessment during modifications of existing process, control or safety systems
  • Examine alternatives in design, with a quick and quantifiable method during the conceptual process design.
  • Aid in designing an "inherently safer" process
  • Proven to identify previously hidden hazards and resolving disagreements on process hazard analyses by providing objective risk criteria.
  • Determines the required Safety Integrity Level (SIL) for Safety Instrumented Function, and is a valuable tool for the safety system lifecycle.
  • Helps identify "safety critical" equipment and maintain optimised numbers.
  • Can be used to highlight important operator actions and responses critical to safety, and highlights areas requiring focus e.g. training, testing etc.

Example LOPA assessment sheet

How to utilise LOPAS throughout the duration of the lifecycle?

The primary aim of the LOPAS software is to ensure that there are sufficient levels of protection against any particular accident scenario. The technique ensures a consistent basis for judging whether there are sufficient numbers of independent protection layers. Inherently safer design can also be analysed. LOPA is not a fully quantified risk assessment approach; it is a simplified semi-quantitative technique which aids in judging between alternatives in risk mitigation. Using the technique improves Hazard Evaluation meeting efficiency, enabling decisions to be reached quicker and therefore ultimately keeping time costs to a minimum.


"Onion" Diagram of Typical Layers of Protection on a Plant

How does the LOPAS software work?

The LOPAS software allows assessments to be performed and documented quickly and effortlessly. Individual LOPA assessments can be grouped to obtain an overall risk value which can be quickly assessed against criteria. The flexible software outputs allow export of assessment results to match the CCPS format, IEC 61511 format or other company specific formats.

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