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Layers of Protection Analysis


LOPA is a simplified risk assessment method. It provides an objective, rational and reproducible method of evaluating the risk of hazard scenarios and comparing it with risk tolerance criteria to decide if existing safeguards are adequate, or if additional safeguards are needed.

LOPA is performed as part of PHA, or after PHA has been completed, and can be viewed as an extension of it. Typically, high risk scenarios are first identified for consideration. LOPA addresses safeguards that are Independent Protection Layers (IPLs), defined as those whose failure is independent of any other failures involved in the scenario. Qualifying safeguards as IPLs and assigning their probabilities of failure is a key part of LOPA. These probabilities are combined with the frequency of the scenario initiating event and the probabilities of other scenario elements to estimate the scenario risk. Layers of Protection Analysis (LOPA) is a risk assessment technique that is a bridge between qualitative PHAs and quantitative risk assessments. Using an accident to consequence scenario, LOPA will provide an estimate of risk on an order of magnitude. Occasionally, we will utilize LOPA in conjunction with a PHA to determine the safety integrity level for a safety instrumented system. Our consultants have extensive experience leading PHAs including HAZID, HAZOPs, What-If, What-If/Checklist, LOPAs, SIS, SIL, combined HAZOP & LOPA, combined HAZOP and SIL, as well as FMEA and FTAs.



Services Offered

  • Development of a LOPA Program.
  • We develop LOPA programs tailored to the needs of an individual company. Programs cover issues such as the LOPA approach to be used, risk criteria to be used, screening PHA scenarios, guidance on when to use LOPA, etc. Program documentation is provided.
  • Development of LOPA Guidelines.
  • We develop technical guidelines for performing LOPA tailored to the needs of an individual company. Guidelines address topics such as failure data to be used, standardizing IPL PFDs, guidelines for qualifying IPLs, etc. A set of written guidelines is provided.
  • Facilitation of LOPA studies.
  • We facilitate LOPA studies as part of PHA studies or as separate studies. We provide a report documenting the results of the study.
  • Development of Risk Tolerance Criteria.
  • We assist your organization in the development of individual and group risk tolerance criteria suitable for your facilities.


Other information

Why Perform LOPA?

LOPA is used to determine the Safety Integrity Levels (SILs) required for Safety Instrumented Functions (SIFs) in Safety Instrumented Systems (SISs) to comply with the ISA S84 / IEC 61511 standard.
LOPA is also used to provide a more rational and objective approach than the subjective engineering judgment used in PHA to decide if additional safeguards are needed to protect against accident scenarios. The subjective approach used in PHA can lead to disagreements and possibly inappropriate measures to reduce risk which is of particular concern when considering risk remediation measures for high risk scenarios, or those that are expensive to implement.”