Fire from a LH2 trailer

An empty LH2 trailer was travelling back to the base to load new LH2, when one of the truck tyre (the inner tire on the driver’s side rear axle) blew causing sparks and smoke. The driver pulled over to the side of the highway and tried to extinguish the starting fire by a fire extinguisher. Since was not able to extinguish completely the fire, he reported the incident to the emergency number. Due to the heat of he fire, the pressure rose inside the LH2 tank and the Pressure Safety Valve (PSV) activated releasing hydrogen gas into the atmosphere through the vent stack. The vented hydrogen ignited, developing fire at the vent stack. The first responders were able to extinguish the fire by using a helium fire abatement system. Meanwhile the pressure inside the trailer had decreased below the PSV activation value, however the PSV did not reseat. Therefore, the hydrogen continued to slowly escape out of the vent stack. 6 hours later, a company employee arrived to the site performed a controlled venting, to reduce the pressure to a safe level and to allow the PSV to reclose. The intervention was successful and the pressure reduced from approximately 170 psi (11.7 bar) to 3-5 psi (0.2 – 0.3 bar).

The INITIAL CAUSE was a conventional fire on a truck tyre, which increased the temperature and consequently the pressure of the LH2 tank. The pressure control system of the trailer functioned as expected. The fire fighting strategy was successful. Nevertheless, regular inspections, and maintenance and replacement procedures are in place for critical components of heavy duty vehicles. 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.

burst disc, vent

A conventional fire started on the truck, initiating the series of events.

DESCRIPTION OF THE UNIT The nominal capacity of the trailer was 10500 gallons (2800 kg of LH2)

The LH2 was almost empty. 80 kg were assessed as vented.

The driver called the alarm number because he was not able to extinguish the tyre fire. Meanwhile the LH2 tank over-pressurised, the pressure relief valve activated and the escaping hydrogen ignited. The first responders were able to extinguish the fire by using a "helium fire abatement system'. The source does not specify what this system consists of. It may implies the use of a non-freezing inert gas system. Anyhow, they avoided the risk of blocking the pressure relief valve due to water freezing. 6 hours later, a company employee arrived to the site performed a controlled venting, to reduce the pressure to a safe level and to allow the PSV to reclose. The intervention was successful and the pressure reduced from approximately 170 psi (11.7 bar) to 3-5 psi (0.2 – 0.3 bar). During the incident, the highway was closed in both direction. The trailer was moved off of the interstate 9 hours after the start of the incident, and the traffic resumed a couple of hours later.