Layer of Protection Analysis

LOPA is a semi-quantitative risk analysis technique that defines a cause-consequence scenario and estimates the likelihood of the undesired consequence from occurring. Layers of protection are added to a system to lower frequency of deviations and mishaps. The combined effect of the protection layers to reduce frequencies and consequences are compared with risk tolerance levels for the plant.

The measure of the risk associated with a scenario depends on the frequency of the initial event and the Probability of Failure in Demand (PFD) of the layers of protection, but for most of industries, this information is sometimes uncertain, imprecise, qualitative or sparse. Therefore some auxiliary methods should be used to complement LOPA in risk analysis. Center’s research includes exploration such auxiliary methods such as the Fuzzy Logic theory and Bayesian estimation, to combine with LOPA to analyze risk in LNG Industry and Ammonia Refrigeration Systems

Layer of Protection Analysis (LOPA) applied to Ammonia Refrigeration Systems

Ammonia is a common refrigerant in the industry. It has excellent thermodynamics and thermo physics properties but it is flammable and toxic. Even though the refrigeration system is simple, when released refrigerant ammonia has caused injuries and fatalities. Layer of Protection Analysis (LOPA) is a semi-quantitative risk assessment technique. This methodology defines a cause-consequence scenario and estimates the likelihood of the undesired consequence from occurring. LOPA helps to determine if the risk has been successfully mitigated with an adequate number of Independent Protection Layers (IPLs).

This research applies LOPA using the framework for an expert system developed by Markowski, and Mannan. In addition, fuzzy logic is used to evaluate the initiating event frequency, the probability of failure in demand for the IPLs and the risk for the scenarios. The main tasks to accomplish are development of incident Scenarios, evaluation of severity of consequences, identification of the layers of protection for ammonia refrigeration systems, and risk estimation for the scenarios.

The final goal is to obtain a framework that simplifies the application of the LOPA technique to Ammonia Refrigeration Systems.

Bayesian-LOPA Methodology Development for LNG Industry

  • Application of Bayesian logic and LOPA in LNG facility