A hydrogen leak and subsequent explosion occurred when tie-downs on a hydrogen transport trailer securing hydrogen cylinder packages failed. The tie-down failure caused the hydrogen cylinder packages to fall off the trailer and eject some cylinders onto the roadway (see Figure 1). The cause of the accident is unknown, but it appears to be unrelated to hydrogen (i.e., likely tie-down strap weakness or error in properly securing tie-downs). The cylinders contained compressed hydrogen gas at 200 bar (2900 psi). The accident caused some hydrogen cylinders to leak and the associated cylinder package plumbing systems were breached. A spark or other local heat source (e.g., from a nearby vehicle motor) ignited the leaking hydrogen and caused a deflagration/explosion that damaged a car following the trailer and broke windows in a nearby house. Emergency crews arrived at the accident scene and cooled the hydrogen cylinders with a water stream to reduce their temperature. No injuries resulted from this accident.
- A hydrogen tube pressure indication system needs to be developed that is robust enough to withstand an accident, indicates hydrogen pressure regardless of valve position, and would be visible from a safe distance during an accident situation. Hydrogen system pressure is very important in determining incident response actions. Centralizing the system pressure indicators on a highly visible information panel located in a protected area of the hydrogen cylinder package is a possible solution to increase visibility.
- Hydrogen valves should have a visible means to show that they are in the closed position. A highly visible lock or pin that can only be used when the valves are closed may help guarantee valve closure prior to transport. If the valve positions are visible, an operating procedure could be added that requires a final valve line-up check just prior to transport trailer departure.
- Hydrogen cylinders grouped together and secured for transport as packaged assemblies should be designed for potential accident conditions. The package tie-down system should be designed with adequate safety margins to assure that hydrogen cylinder packages remain secured to the transport trailer under adverse conditions. However, the package design should assume that the package might fall from a moving transport vehicle and impact the ground, but the hydrogen cylinders should still be contained within the package. A program to test hydrogen cylinder packages under hypothetical accident conditions would be useful for developing designs that could be certified to survive potential accident conditions.