LESSON LEARNED:The technician involved in the incident was a very experienced operator, since years responsible not only for the hydrogen storage facility, but also for all fuel cells and electrolyzers testing laboratories. Since the start of the incident sequence, the technician acted timely and effectively to reduce the risk (interruption of the hydrogen main supply, realisation of the presence of a flame, use of local fire extinguishers, call of the fire brigade). Nevertheless, the operation which brought to the incident was not part of the normal practices and not explicitly covered by risk assessment and the safety measures put in place for the laboratory operation. Moreover, the incident revealed the difference between theoretical knowledge of the possible risks and consequences, and the practical realisation of the same. The two following facts are worth a mention: the possible existence of a completely transparent hydrogen flame was not considered as a possibility by the technician at the start of the chain of events. He realised this possibility only when he felt by hand a temperature increase on the pressure regulator, and saw the development of fumes on the tank. To stop the supply of hydrogen from the storage to the tank, he moved to the control panel of the storage facility, installed at the wall behind the cylinders bundles. In this way, he has been able to minimise the total release of hydrogen, and excluded the possibility of consequences escalation. However, he put himself in a dangerous situation, trapped between the wall and the hydrogen flame, instead of stepping away of he facility to a safe distance. CORRECTIVE ACTIONS(1) The safety measures in place in the storage facility have been thoroughly reviewed, including the standard connection procedures.(2) A basic training was provided on compressed gases handing, including how to deal with pressure reduction devices, not only to technician directly involved with hydrogen, but to all technicians on site. A list of additional, more advanced and more specific exercises has been collected and sent for prioritisation to the training officer. (3) The refilling of bottles provided by customers and for customers use has been prohibited at the storage facility. The reason is that it is impossible to independently control and assess the quality of the components delivered, often manufactured by different 1st and 2nd Tier producers and assembled by customers. (4) For the regular use of hydrogen by G.I.4 laboratory, other, safer solutions shall be used (for example the delivery of already filled cylinders with the required size by a contractor). (5) The possibility of filling hydrogen cylinders at the storage facility for JRC-internal purposes will be maintained, but it will remain a special operation, to be executed ad-hoc, when special circumstances requires it. (6) Therefore, a dedicated Task Instruction document will be prepared beforehand for the activity at (5), describing in detail the series of actions required. Only components will be used certified according to the European Pressurised Equipment Directive. The Control Panel will be also placed in the most favourable place to facilitate a quick evacuation. (7) The Task instruction will explicitly mention that the filling can only be performed by directly connecting the hydrogen storage system to the receiving cylinder by means flexible connector (cascade filling), without the use of pressure regulator or other pressure conditioning systems.