This case study demonstrates an effective incident investigation approach to identify system-related root causes. The premise is simple: "What people do makes sense to them at the time." The approach combines human error concepts and human factors analyses. The combined approach helps define and eliminate "hindsight bias" (the investigator's bias that exists because of the known bad consequence). The case study's human error mistake was simple and straightforward; however, it failed to capture the role that previous decisions played in the incident. The team's original recommendation was to "be more careful next time." However, a deeper process safety management system-related issue was uncovered by continuing the probe using the human error "root cause" as the starting point of the investigation. This is the point where the real systemic issues are found. This case study showed how poor communications between the different people involved with engineering design, contractor fabrication, equipment inspection, and subsequent site installation caused the incident. The final recommendation of the team was to link the separate management of change (MOC), prestartup safety review (PSSR), and mechanical integrity quality assurance-related efforts together, ensuring an inspection step for "replacement-in-kind." In conclusion, the combined approach helps the team better understand the timing and conditions of the event, better understand why people make the decisions they make at the time the event unfolds, and ensures that systemic root causes are discovered so that more appropriate, system-related preventive measures are chosen and implemented. (C) 2011 American Institute of Chemical Engineers Process Saf Prog 30: 372-376, 2011