What were the causes of the 2019 explosion at the Korean research facility involving an electrolyzer and what were the lessons learned about design?

The suspected cause was a mixture of oxygen and hydrogen that passed downstream from the electrolysis unit into several storage vessels. Hydrogen-oxygen mixtures are very hazardous. Subsequent ignition resulted in internal pressure that exceeded the limits of the storage system. The design of electrolyzers, detection of upset conditions, and preventing the accumulation of oxygen within the hydrogen system is important for safe operation.