Conventional fire on a CGH2 tube trailer

A tube trailer was driving on a highway, when the drivers noticed in the back camera smoke coming from the rear of the vehicle. After stopping the vehicle on the shoulder, they discovered a fire from the trailer's right rear inner tyre.
They attempted unsuccessfully to extinguish the fire using two on-board fire extinguishers. They driver notified the city fire department and the fire brigade arrived about 10 minutes later.
They succeeded to extinguish the fire in two hours and 50 minutes. The compressed hydrogen tube was made of carbon composite, and it was affected by the fire, probably starting burning. Because of this, or simply because of the raise in temperature, the fusible plug safety valve (TPRD) activated and released the hydrogen. The KHK report assumed a release without ignition.

The INITIATING CAUSE was a conventional fire on a tire of the truck.
The safety system functioned as designed. The thermally activated pressure relief device (TPRD) functioned as designed, by activating due to the increased temperature and releasing the hydrogen to avoid a failure of the tube under pressure.
Regarding the ROOT CAUSE, it must first be noted that regular inspections, and maintenance and replacement procedures are in place for critical components of heavy-duty vehicles, such as tyres and brakes. These measures should be able to prevent negative consequences to the rest of the system. This is even more important for hazardous material transports. Shortcoming in these procedures could be suggested as ROOT CAUSE.

TPB, omposite vessel

DESCRIPTION OF THE UNIT
The KHK report mentions only one container. Due to the lack of details, the trailer configuration is unclear, but is very probably a multiple-tube trailer. For example Kawasaki trailer had 24 tubes of type III composites, with 200 l of water capacity each. Till 2013, the nominal pressure was 350 bar. From 2014, it was increased to 450 bar, with a total transport capacity of 260 kg of hydrogen.

The safety system functioned as designed. The thermally activated pressure relief device (TPRD) opened because of the increased temperature and released the hydrogen to avoid a failure of the tube (vessel) under pressure.
The KHK report says that the hydrogen very probably did not ignite. This is a credible scenario, especially if the point of release is far away from the local conventional fire.