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A process hazard analysis (PHA), such as a Hazard and Operability Study (HAZOP), is a useful tool in identifying potential hazard scenarios; however, a PHA can only give a qualitative indication of whether sufficient safeguards exist to mitigate the hazards. Layer of Protection Analysis (LOPA) is a risk management technique commonly used in the chemical process industry that can provide a more detailed, semi-quantitative assessment of the risks and layers of protection associated with hazard scenarios. LOPA allows the safety review team an opportunity to discover weaknesses and strengths in the safety systems used to protect employees, the plant, and the public. LOPA is a means to identify the scenarios that present the most significant risk and determine if the consequences could be reduced by the application of inherently safer design principles. LOPA can also be used to identify the need for safety instrumented systems (SIS) or other protection layers to improve process safety. This paper provides a brief overview of the technique and is intended for a novice interested in the basic principles involved.
Ronald J. Willey (Wed,) studied this question.