Explosion of a tank at hydrogen components manufacturer

The accident happened during testing of a hydrogen tank at a company which manufactured valves and other hydrogen-storage components. A dull bang and a huge pressure wave was felt kilometres away. News report massive damage to the test facility, but a very small fire.
Still according to the news, the most probable cause emerging from the investigation was the over-pressuring of the tank due to an erroneous connection. While the news speak of a connection to a compressed air hose, another source specifies that it has been a 900 bar gas connection to a tank designed for a nominal working pressure of 350 bar. This is the most plausible explanation, by assuming that a pressure test was ongoing, with a inert gas such nitrogen.

The INITIATING cause was the erroneous connection to a pressurised gas source much higher than the maximal pressure of the tank.
The sources report the company statement that material or component malfunctions could be excluded and that the ROOT CAUSE was a human error.
Due to the lack of details, it is not known if the event was the result of not following the procedures, or if there were shortcoming in the procedures, and therefore both causes are attributed to this event .

tank

The tank was being tested. Since this incident seems to be related to high pressure failure only, and not to fire and chemical explosion, it could be assumed that the gas used for testing was an inert gas.

One worker was slightly injured, massive damage to the test facility, a very small fire.