Liquid Hydrogen Release from a Rail Tanker
The whole content of the rail tanker, that is 42,000 l (about 2600 kg) of liquid hydrogen, was entirely lost over a period of seven hours via the venting line of a tank. The accident occurred at a railway station, and the wagon with the tank that had been uncoupled from the goods train and shunted to a siding to allow the release of its content. The cryogenic tank was of the Dewar type with numerous insulating and reflecting layers in its inter-space, kept under vacuum. According to the source referenced, a micro-crack in the outer wall of the tank caused the loss of the vacuum and was the initiating event of the release.The crack caused the loss of the interspace vacuum and of the related thermal insulation function, with a quick increase of the conductive and convective heat transfer between the tank interior and the environment. The liquid and vapor hydrogen raised the internal pressure to the design value of the safe valves (4). The valves are designed to maintain a constant 12 bar pressure differential between the upstream and downstream sides of their shutter (thus the max pressure attained inside the tank during the accident was 13 bar). The calculations of the referred source (Cancelli et al., Cryogenics 2004) shows that:1.The hydrogen temperature raised slowly for the first 2.5 hours, until the moment it reached the critical temperature (Tc). Until that time, the incoming heat was used as latent vaporization heat. After the attainment of Tc, the incoming heat became sensible heat and the temperature raised steeply. 2.The hydrogen flow rate through the safety valves peaked approximately at the same moment (approximately after 2.5 h), corresponding to the moment in which the densities of the gas and liquid phases in equilibrium become similar.
Event Date
July 9, 1991
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
Immediate cause was the cracking of the external layer if the cryogenic tank.A contributing (or root) cause was probably a (materials, safety?) design shortcoming.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
safety valve, Dewar-type tank, railway wagon
Storage/Process Medium
Storage/Process Quantity
2600
Actual Pressure
13
Design Pressure
1
Location Type
Location description
Railway Station, Inhabited Area
Operational Condition
Pre-event Summary
The cryogenic tank was of the Dewar type with numerous insulating and reflecting layers in its interspace, kept under vacuum.
Currency
Lessons Learned
Lessons Learned
The safety design of the tank demonstrated its soundness, because despite massive increase of the temperature inside the tank, the release has been successful and, despite the high quantity, the hydrogen did not ignited. Nevertheless, the cases of loss of isolation need to be studied in detail and the probability of their occurrence further reduced.
Event Nature
Emergency Action
The wagon with the LH2 tank was uncoupled from the goods train and shunted to a siding track of the railway station, till the end of the release.
Release Type
Release Substance
Hydrogen Release Concentration (%)
100.00
Release Duration (s)
25000
Release Rate (kg/s)
0.10
Release Amount (kg)
2500.00
Release Pressure (bar)
13.00
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
News in Newspaper La Stampa 10/07/1991
Presentation at the Seveso III & H2 worksop of 17/09/2023