Using LOPA to examine risk levels of selected scenarios
Managing process safety means understanding the many factors that contribute to risk and establishing appropriate measures for risk mitigation. Layers of Protection Analysis (LOPA) is a method used to evaluate high-consequence scenarios determining if the combination of probability of occurrence and severity of consequences meets a company’s risk tolerance. LOPA addresses the key questions: “how safe is safe enough?”; “how many independent protection layers are needed?”; and “how much risk reduction should each layer provide?”
Our process safety specialists are comfortable with complexity and experienced in implementing the LOPA methodology. We provide rational, semi-quantitative risk-based answers to key questions as well as clarity and consistency among analyses of equipment and processes at plant sites. Documentation of each decision and the decision-making process is an integral part of our methodical approach. Upon completion of the analysis, the LOPA report promotes self-sufficiency by facilitating understanding among site personnel of process hazards and their prevention.
With a strong track-record in process safety, we have carried out countless Layers of Protection Analyses, gathering valuable experience to share with our clients. We place a premium on maintaining a global presence, providing services in a wide variety of languages and having a command of the local codes, standards and cultures. Combined with our intimate knowledge of process safety engineering and process safety data, we offer expertise unrivalled in the market.
A thorough approach to LOPA services
Typically, a high-consequence scenario – which usually involves a combination of equipment and human failures – is identified during a qualitative hazard evaluation, such as a Process Hazards Analysis (PHA) or a Hazard and Operability study (HAZOP). LOPA is then implemented for a closer, more careful assessment of this scenario. LOPA is a quantitative screening tool which provides a consistent, objective, and defensible approach.
A LOPA can be visualized as a series of slices of Swiss cheese, whereby each slice is a layer of protection with a varying number and size of holes representing flaws. A high-consequence scenario occurs only if at least one of the holes in each slice “line-up,” allowing propagation of multiple failures. For components of a process-control system, such as safety instrumented systems and other components such as relief valves and rupture disks, it is important to know or estimate the probability of failure on demand.
We study the process under investigation to identify likely initiating events and estimate the frequency of initiating-event occurrence. We will then examine all process-control features and safeguards, estimating the reliability of protection provided and ensure the independence of each protection layer. With this information, the likelihood of occurrence (or frequency) of a given high-consequence scenario can be semi-quantitatively determined. Combining this likelihood with the severity of the consequences, an evaluation of risk is obtained.
A risk matrix is usually employed to show the possible combinations of likelihood and consequence severity. The risk thus obtained can be compared to the facility or corporation’s risk tolerance for presentation to site and/or corporate management. We prepare a comprehensive study report to serve as a record of the completed analysis, including descriptions of potential risks with the existing safeguards and with recommendations for additional safeguards, where warranted.