The cracked Reactor R2525 initiated the sequence of events which led to disaster. Examination of the crack by expert metallurgists showed that the crack had been caused by nitrate stress corrosion. This corrosion was created because nitrate treated cooling water had been used in the past to dilute some of the process liquids which contaminated the cooling water. The situation is not unique to Nypro's plant and indeed the use of nitrate treated cooling water, contaminated by process liquids, may be common in other plants. The attention of industry should be drawn to the risk.