This article describes the investigation of an incident of catastrophic failure of a primary reformer in an ammonia plant. The lessons learned from the root cause analysis of the event are of interest. The reformer is one of the critical unit operation in an ammonia plant. Under normal operating conditions, reformer tubes get aged and progressively develop "creep" in metal leading to a possible catastrophic failure. This event of total failure occurs when one tube fails and results in destroying the neighbouring tubes. Such a situation may occur during start up. A failure diagnosis model is developed, and several hypotheses were tested to determine most likely causes. The analysis revealed that, due to short supply of nitrogen, the start-up procedure of the reformer was modified on expert's advice shortly before the operation. This change was not reviewed by the whole team. The important parameters in view of the changed procedures were not monitored. This communication gap resulted in severe damage to the reformer melting almost all of the tubes and convection zone coils. It may be observed that the primary reformer amounts to 25% cost of whole ammonia plant. The systematic root cause analysis, thus, clearly identified the reason of catastrophic failure as incomplete analysis and nonconformity of procedures. (C) 2010 American Institute of Chemical Engineers Process Saf Prog 30: 62-65, 2011