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Layer of Protection Analysis - Introduction


Art M. Dowell (Chemical Process Safety Consultant and Rohm and Haas, retired)


Layer of Protection Analysis (LOPA) is a semi-quantitative tool for analyzing and assessing risk that has gained acceptance in the Chemical Processing Industries (CPI) and has risen to be one of the leading risk assessment techniques used for process safety studies. LOPA generally employs more rigor and science than what is encountered with qualitative risk assessments but is less demanding than a detailed Quantitative Risk Assessments (QRA).

LOPA uses simplified methods to characterize the consequences and estimate the frequencies in the risk assessment process. To lower the frequency of the undesired consequences, layers of protection can be added to a process including: inherent process safety; the basic process control system; safety instrumented functions; passive devices, such as dikes or blast walls; active devices such as relief valves; and human intervention. The primary purpose of LOPA is to determine whether there are sufficient layers of protection against a specific accident scenario.

This product discusses important LOPA concepts, such as, a) rules for independent protection layers (IPL), b) basic process control systems (BPCS), c) safety integrity levels (SIL), d) methods for calculating mitigated consequences, and e) advantages of LOPA. An example using LOPA on a distillation column is included. This product assumes that students are familiar with process hazards analysis (PHA) techniques such as HAZOP and is intended for undergraduate students (especially in design courses) and practicing engineers interested in using LOPA.

Student access: An introduction and references are available to students through the site.

Suggested courses that can use this product

  • Design
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