Fire on a CGH2 tube trailer

A fire developed on a tube trailer transporting 330 kg of compressed hydrogen, while travelling on a highway. The truck had left a plant of hydrogen production and storage to deliver to a refuelling station.
The probable origin of the incident was a fire on the rear tyres of the trailer, which caused the overheating of the tubes, increasing the internal pressure and the consequent opening of the pressure relief valve.
The investigation determined that the released hydrogen ignited twice, forming a jet flame. This suggests that only two of the tubes had the pressure relief valve activated. In the video, only one flame is visible. The flames reached 10 to 20 m. The fire brigades were able to extinguish the file in 30 minutes.

The INITIATING CAUSE was a conventional fire which triggered the activation of the safety device of two of the hydrogen tubes when their internal pressure rose due to the increased temperature.

The ROOT CAUSE is of difficult attribution. Nevertheless, considering that such a scenario must be prevented, the design of the trailer-tractor system would need improvement and the inspection and requalification procedures for trucks carrying hazardous materials made stricter.

tube trailer truck, brakes, 10 hydrogen tubes.

DESCRIPTION OF THE UNIT
The trailer cargo consisted of 10 tube, each with ha volume of 2.3 m3 at a pressure of 20 Mpa.
At the front of the trailer 10 burst discs are installed, one for each of the tube, connected to a vent pipe releasing the gas in a almost vertical direction, above the full extension of the trailer.
At the rear additional 10 burst discs are installed, and a safety valve common to the whole pipe connections.

If only one tube vented, a loss of 33 kg occurred and contributed to ignition. For two tubes, this would be 66 kg. Nevertheless the loss of the total load is reported in HIAD, because the most ptobable emergency action before tansporting away the trailer has been the full release of tubes content.

The Ministry of Trade, Industry and Energy called a meeting to discuss the improvement of the system. The meeting was attended by officials from the hydrogen transportation industry.

In this event, the hydrogen-related safety measures worked as designed, the burst discs activated releasing hydrogen from the tubes under overpressure. The released hydrogen produced a jet flame directed upwards, so that did not cause a hazard to the traffic at street level.

However, an accidental scenario involving fire when transporting by road trucks hazardous (flammable) materials should be prevented as far as possible. Therefore, the inspection procedures on those trucks should be improved (for example in the frequency of the checks, or by stricter control of materials used, or with higher frequency of replacements of consumables, etc.).
Moreover, the safety design of the overall trailer-tractor system should be improved, to protect better the compressed hydrogen tunes in case of conventional fires.


Finally, the pictures delivered by the KBS News show that truck took fire in front of a tunnel. If the incident would have occurred in the tunnel, the consequence would have been much more sever. A hydrogen-specific regulation for the use of public infrastructures lacks in most of the countries. The pre-normative research project HYTUNNEL has studied in detail the consequences of different release and ignition scenarios in tunnel (https://hytunnel.net/)

Hydrogen transport vehicles are subject to regular inspections every two years in accordance with the Motor Vehicle Management Act, and hydrogen containers loaded into vehicles are subject to initial inspection and periodic (5 years) re-inspection when newly manufactured in accordance with the High Pressure Gas Safety Management Act.
As a result of the accident investigation, some improvements were proposed:
(1) improving the direction of the hydrogen outlet
(2) strengthening the heat insulation of the hydrogen container by installing a fireproof mudguard to block the heat of the hydrogen container in the event of a tire fire.
(3) review performance inspection of safety devices and container inspection in accordance with laws and regulations,
(4) perform awareness and training for driver.