(18c) Incorporating and Quantifying Human Activities and Actions In Layer of Protection Analysis

Layer of Protection Analysis (LOPA) has now been used throughout the chemical process industries for a number of years. It seemingly continues to gain popularity, due to its simple approach to risk with a scenario-based methodology and its ability to assist in decision making. The intended application of LOPA by companies may vary somewhat, but is commonly used as a simplified semi-quantitative risk assessment method to determine if Independent Protection Layers (IPLs) are sufficient in number and rigor, to determine potentially required Safety Integrity Levels (SILs) for Safety Instrumented Functions (SIFs) and resultant Safety Instrumented Systems (SISs), and to determine if the risk is initially low enough or has been made so through planned changes. The human role as a potential initiating event or as part of a protective layer is important in the chemical process industries generally, and plays an even more significant role in batch processing facilities. Human activities as potential initiating events and within human independent protective layers (IPLs) are reviewed and methods for quantification outlined ? including an extension beyond LOPA into human reliability analysis and methods to ensure that human error probabilities (HEPs) are specific and suitable to the operations and process safety culture at a given plant site.