Conventional fire on a CGH2 trailer

A CGH2 tube trailer-tractor was travelling to deliver hydrogen to a customer, when a fire developed on right side of the tractor around the rear of the hood and passenger side door. Very quickly the entire power unit was engulfed in flames. The driver called 911. The highway was closed. Approximately 30 minutes later, the fire had spread to the tractor drive tires on the passenger side causing extreme heat on the bottom tubes of the trailer. Hydrogen began to leak and ignited. The fire continued to burn slowly until customer personnel lowered the pressure in the tube, which stopped the flow of gas and the fire self-extinguished. The units were released to a towing company approximately 7 hours later.

The INITIATING CAUSE was a conventional fire from tractor components (similar incidents reported the brakes as the source of the over-heating). The fact that the burst discs did not appear having failed indicated that the pressure inside the tubes was not affected by the heat. It has been preliminary concluded that a component part of the pressure control system of the tube failed under fire or heat, very likely the bull plug of one of the tube, and more specifically the seal between the bull plug and the cylinder end melted and caused the leak. It indicate as ROOT CAUSE a safety design unable to consider this type of fire and to protect critical component from it.

seal

DESCRIPTION OF THE UNIT The trailer was carrying 10 tubes. On each tube end, a bull plug was installed, with an internal burst disk assembly screwed into it. The hydrogen trasport capacity was 325 kg The transported quantity when the incident occurred was 255 kg

only a limited amount of hydrogen was lost: the PHMSA source reports 5 kg.

The fire continued to burn slowly until customer personnel lowered the pressure in the tube, which stopped the flow of gas and the fire self-extinguished.

The conventional brake fire which started this incident did not produce a heat input to the CGH2 tubes to cause their internal pressure to raise above the limit set by the pressure relief system. The burst disc did not open. The only damage caused by the fire was to a seal fitting, which caused a leak with limited consequences. Nevertheless, other cases started with conventional fires caused the venting of the whole hydrogen load, because the pressure relief valve were not activated. Such a scenario must be avoided when the trailers are in a confined space, such as a tunnel. Moreover, tubes components critical to safety shall be well protected from fires and heat. Finally, better quality control and inspection are required for conventional components of a truck, which may play a critical role in affecting the hydrogen load transported. A conventional fire on brakes could cause a total loss to the vehicle, but in presence of a flammable gas, it could have much heavier consequences.