Layers of protection analysis for human factors (LOPA-HF)



Process hazard analysis (PHA) performed to meet the requirements of OSHA and EPA regulations must address human factors. Both the human failures that can cause accidents and the human factors that can influence them must be addressed. This is important because it is generally believed that 50% to 90% of process accidents can be attributed to human failures. Human failures are usually identified in a PHA by simple brainstorming. However, PHA teams have a tendency to focus on equipment failures. A better approach is needed. Common approaches for identifying the human factors that influence human failures involve the use of checklists during the PHA. Unfortunately, these approaches have proven problematic. There is a need for an improved method that is both efficient and effective in helping to control process risk.

This paper describes improved approaches for identifying human failures in PHA and human factors issues that impact on the hazard scenarios identified by PHA. The former is accomplished using an approach that conceptually identifies human failures in a manner analogous to generating deviations in a hazard and operability study. The latter is achieved by the application of the framework and methods of Layers of Protection Analysis (LOPA), a simplified risk assessment method. These approaches are described and illustrative examples are provided.