[NOTE: the sources are not completely clear in describing the system involved in this incident ; the following is the most plausible option according to HIAD validator]The explosion happened in two hydrogen tanks ('receivers') whcih were receiving and storing hydrogen produced by a water electrolyzer via two compressors. The hydrogen was then supplyed to a further non-specified generator. The plant had been shut down on August 24 to 26 and resumed the hydrogen production and storage on August 27. On August 28, after that the tanks had supplied hydrogen to the generator for 20 hours, the hydrogen purity in the generator dropped suddenly to 85%. The two tanks were disconnected for hydrogen purity sampling and the generator was further supplied with standard hydrogen bottles. The quality check indicated a purity of 95%. One of the two tanks was then re-connected to the electrolyzer after approximately 7 hours. Again, the purity in the generator indicated 85% hydrogen purity. 20 minutes later, both tanks exploded, resulting in two fatalities, 18 injured by fragments and extensive blast damage in a 100 m radius. An investigation from the incident reported that all the gas supplied to the receiver over a 20-hours period had been air. The explosion has been assessed at TNT equivalent 275 kg.