A spill of concentrated hydrochloric acid caused considerable damage at an ion exchange resin regeneration plant. The release was caused by two independent failures: the failure of a diaphragm pump and a containment dike. An accident investigation determined the root causes of the accident and evaluated the system safety of the process. The root cause of the diaphragm pu mp failure was environ mental stress cracking of the PTFE diaphragm in 33% HCl service. the root cause of the dike failure teas insufficient steel reinforcement . Based on the accident investigation, additional safeguards were implemented to prevent a recurrence of the accident.