Safer design of process equipment can protect against unexpected events. Two case studies involving the design of a process vessel and the subsequent events will be reviewed. One case study will show how the original design minimized equipment damage from an operational error, and how additional safeguards will prevent recurrence. The second case study will show that over time small process changes can lead to an unexpected chemical reaction that results in a vessel rupture. We will also cover the additional safeguards added to prevent recurrence. (C) 2004 Elsevier B.V. All rights reserved.