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).
Near the end of the process of filling a gaseous hydrogen tube trailer at a liquid hydrogen transfilling station, a safety pressure-relief device (PRD) rupture disc on one of the tube trailer’s ten tubes burst and vented hydrogen gas. The PRD vent tube directed gas to the top of the trailer where the hydrogen vented and ignited, blowing a flame straight up in the air. The operator filling the tube trailer heard a loud explosion from the sudden release of hydrogen gas and saw flames immediately.
An operation to increase the pressure within a hydrogen tube-trailer to 6000 psig was in progress when a burst disk failed at approximately 5200 psig and hydrogen was released. A vent line attached to the burst disk was not sufficiently anchored and bent outward violently from the thrust of the release over an approximate 4-inch moment arm, causing considerable damage to the adjacent vent system components. The operation is conducted with personnel present, but fortunately no one was in proximity when the burst disk failed.
In early afternoon, a northbound tractor-semitrailer with horizontally mounted tubes filled with compressed hydrogen at approximately 2400 psi (166 bar) was struck by a northbound pickup truck that veered into the semitrailer's right rear axle. According to witnesses, the tractor-semitrailer then went out of control and left the roadway, coming to rest approximately 300 feet (91 meters) from the point of impact. As a result of rotational torque and impact, the end of one tube was sheared off at the bulkhead and left the tube bundle.
A pressure relief device (frangible burst disk) on one of a hydrogen delivery tube trailer's 26 tubes failed prematurely and released hydrogen while filling a hydrogen storage tank at a government facility (see Attachment 1). Prior to the filling process, all procedures and safety checks, including connection to the facility's regulator/distribution control system with leak checking and follow-up verification of leak checking by facility personnel, were completed (see Attachment 2 for more details).