CGH2 tube trailer explosion

An explosion occurred on a tube trailer when two operators were working on it. 
There is limited information on the accidental sequence, but visual information provided a video (see link to source), allows for the following preliminary conclusions.

The compressed hydrogen storage unit transported by the trailer had horizontally placed tubes, connected via a system of piping and valves. There were two storage units on the same trailer. The transport capacity of such a system could be assumed not higher than 500 kg of hydrogen (i.e. max 250 per unit). Three trailers were parked near each-others. The one affected by this incident was the only one connected to a tractor. 

it is plausible to assume that a release of hydrogen occurred during or just before a maintenance action taken by the drivers. Because the tubes were confined in a metallic box, hydrogen could cumulate inside the unit. The hydrogen then ignited and due to the confined or semi-confined condition of flammable cloud, it exploded. The roof of the rear unit appears bent outwards, together with at least one side panel. The second unit of the trailer appears also damaged by an internal explosion.  
A fire followed, which affected the second trailer. One of the videos shared by the police shows a series of vertical jet flames, very probably the consequence of the opening of each of the pressure relief valves under the effect of the initial fire. 

The fire brigade was able to extinguish the fire in 20 minutes with water.  

The explosion caused one fatality and one injury. 

The INITIATING and the ROOT CAUSE are unknown. 
The scarce information do not allow to know if the hydrogen release was caused by a leak on one of the piping connections, or a consequence of the intervention of the drivers. The quantity of hydrogen released and ignited in the fire are unknown. 

tubes, trailer

One driver died during the explosion, the other was first hospitalised with sever burns.
Waiting for the result of the investigation, the whole fleet was grounded. Consequently, over 60% of California hydrogen stations was put offline after hydrogen supply disruption.