Vipsit has also experience performing LOPA analyses.

The Layer of Protection Analysis (LOPA) technique augmented with Safety Integrity Level (SIL) or Safety Instrumented Functions (SIF), is a robust risk management strategy and an internationally recognized risk assessment method based on corporate tolerability criteria, used mainly in the large scale process industries as a risk assessment tool. It is a sibling to the Bowtie and HAZOP method. The LOPA analysis is typically done in an excel sheet, where the columns are: A: initiating event, B: Probability; C, D, E, F: Consecutive layers of protection; G: Consequence, H: Final Probability.

Although this method uses probabilities and does build on mathematical models and number crunching, it is still not considered as a fully quantitative risk assessment tool, only a semi-quantitative one. In other words, it is a simplified risk assessment method that provides a middle ground between a qualitative process hazard analysis and a traditional, quantitative risk analysis. The reason for this is that some of the probabilistic values may be estimates, rather than empirical measured values. The LOPA analysis uses simplifying rules to evaluate the initiating event frequency, the independent layers of protection and consequences to provide an order of magnitude estimated risk.

In order to prevent unwanted incidents, mitigation measures are put in place. Like the Bowtie analysis shows, these measures can either regulate the likelihood or the consequence. When considering layers of protection and safeguards we apply a number or an efficiency rate to the different mitigation measures and multiply those to get the final protection factor for a given incident.

There are different types of software that can facilitate the visualization of LOPA and Bowtie Risk Analyses. The software is fairly intuitive and with a little practice fast to use. Alternatively these types of pictures can be generated in PowerPoint, Visio, SmartDraw and similar software packages.

It is important that the layers of protection are truly independent of each other, with no interdependent behavior. The correct cause-consequence pairs must be identified for analysis. These cause-consequence pairs are the outcome of another assessment technique as a HAZOP or a SWIFT analysis. Only then will meaningful information be generated that can be used in the LOPA analysis

Technical equipment can pose a safety risk so dangerous that people should not be exposed to the equipment. In such cases, the relevant risks must be reduced to meet the need for safe operation. It must be possible to quantify (and measure) risk reduction in order to satisfy this requirement. This is achieved using the SIL “unit”, whereby only whole values are defined within a range from 1 to 4, where SIL 4 is the most dependable and SIL 1 the least. A SIL is determined based on the number of quantitative factors in combination with qualitative factors such as development process and safety life cycle management.

The process follows the AMP model, Assessment, Mitigation and Performance.