C LH Accidents in Three Hydrogen Plants

Edeskuty [56] summarizes three hydrogen accidents related to liquid hydrogen (LH2), i.e.: (1) minor explosions in a hydrogen vent system, (2) combustion of hydrogen in the open atmosphere, (3) liquid hydrogen dewar storage explosion.

In the first accident, several explosions occurred in a liquid hydrogen facility consisting of 15,000 kg of LH2. All of the hydrogen vents were manifolded into a common vent system terminating in a flare stack. During no operation of the system the liquid hydrogen was venting the normal boil-off through the lighted flare stack. The accident was initiated a few minutes after a technician removed one of the check valves leading into the vent system from a source other than the two dewar. Fortunately, there were no injuries. Edeskuty [56] concluded that it is the best not to join separate components of a system to a common vent line when there is any possibility of interaction.

The combustion accident occurred in an experimental facility while the sound level of a rapid flow of hydrogen was measured. The hydrogen was obtained as liquid hydrogen and converted to high-pressure. The hydrogen entered the piping system connecting the hydrogen supply tanks to the discharge nozzle at 23 MPa, and at ambient temperature. The unplanned ignition occurred after the hydrogen flow was reduced to 16 kg/s ( from 55 kg/s). It was estimated that about 90 kg (10% of the total hydrogen vented) participated in the combustion. The closest observers, located 600 m away did not detect a pressure wave, however, windows were rattled in a building about 3200 m. Away from the extent of damage, it was estimated that the buildings had experienced an overpressure of 1.2-2.4 kPa. Edeskuty [56] concluded that it is very difficult to eliminate all ignition source from rapidly venting hydrogen.

The explosion occurred in a LH2 storage dewar used to supply gaseous hydrogen (GH2) to a semiconductor building. It caused property damage and injury to five persons in the vicinity of the dewar. The dewar has a capacity of 34 m3 (2000 kg) and a working pressure of 1.03 MPa. The accident occurred about 2 days after the dewar was filled from the LH2 supplier. Some possible causes of the accidents were attributed to an H2-O2 reaction, breaking of the vacuum. What happened exactly is uncertain, but it was speculated that a partial blockage in the vent line prevented adequate venting of the high boil-off rate after insulation vacuum was broken. Te resulting pressure buildup in the tank caused its rupture. Five persons were injured. They had skin burns (some third degree), shrapnel wounds, and blast effect wounds. Conclusions drawn in [56] include: (1) redundant instrumentation is recommended to provide an adequate, and believable, indication of actual operating conditions; (2) more than one vent point should be provided because the failure of a single vent could result in damage to the equipment and injury to personnel; (3) advance emergency planning should address appropriate actions to be taken in the event of possible emergency conditions; and (4) no action should be taken until the total consequences of that action have been thoroughly evaluated.

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