Explosion on a CGH2 cylinders bundle during filling

A compressed hydrogen container was being filled at a refuelling station. The container was belonging to a trailer and consisted in a bundle of tubes connected via piping to a manifold and filling port.
The filling operation was ongoing since approximately one hour, when an employee performed an inspection to the filling. He confirmed the existence of a hydrogen leak. An explosion followed when the employee still on location. He opened the main valve of the sprinkler system and started sprinkling water. Surprisingly, the hydrogen detector did not issued any alarm.
Another employee in the control room heard the explosion and the consequent vibrations, and requested the stop of the compressor and notified the fire department. The first employee returned to the control room and pressed the emergency stop button.
The fire brigade created a security perimeter and extinguished the fire.
The post-incident investigation concluded that the leak occurred at a brazed connection, along the piping from the manifold to the individual tube. The failure had been caused by an effective design, which allowed for mechanical fatigue of the brazed joint at every filling cycle, due to the weight of the filling port/hose.

The INITIATING CAUSE was a cracked pipe connection.
This crack had already been discovered and repaired by the owner, but the repair revealed being inadequate, because the defect had reformed due mechanical overload occurring every time that the manifold was connected to the filling port.
The ROOT CAUSE was a design failure of the manufacturer (the defective connection structure was not properly fixed and was over overloaded during filling) and a shortcoming of the management of the refuelling station (the acceptance procedure of the container to be filled was not robust enough to refuse refuelling in case of defects).

weld, connection, pipe

DESCRIPTION OF THE FACILITY
From the pictures provided by KHK, the container (bundle) appears to be made of 6x5 horizontal tubes. It was filled in a boot protected by walls on three sides.

Sever injuries

To prevent the recurrence of a similar accident on all the containers of the dame type (15), the operator of the filling station held discussions with hydrogen cartridge owners. The modification of the filling port was required, to avoid that a load is placed on the piping. Moreover, the manifold had to be re-designed in accordance with the Japanese High Pressure Gas Safety Act .
The following actions and procedural modifications were adopted.
(1) The inspection checklist required for the acceptance of the trailers, will contain a specific item dedicated to the inspection of the manifold and the filling nozzle. In case of discovery of a defect, it will be necessary to clarify with the owner the procedure to repair it. A written confirmation from the owner on the correctness of the repairs will be required.
(2) Before filling the trailer containers, it will be necessary to perform an airtightness test of the system at filling pressure.
(3) The emergency response procedure was modified: in the event of a large hydrogen leak, an immediate emergency shutdown will be required.
(4) To improve the effectiveness of gas detection and to guarantee early detection, the number of gas detectors for bulk cylinders and trailer containers was increased. They will have to be install them in the most appropriate locations for early detection.
(5) Immediately after the incident, all managers and workers of the facility visited the accident site and held a safety discussion. Regular education and training will be provided to workers, including the mentioning of this specific incident, to guarantee that the lesson will not be forgotten.
(6) The management processes will be revised and thoroughly implemented.
(7) The procedure regulating the work of third parties will also be reviewed and agreed with them.