Water Electrolyzer Explosion
The incident occurred during the verification operation of a new high pressure hydrogen generator. The electrolysis cell burned down, the pipes of the oxygen circuit burst and the peripheral equipment were scattered all over the facilities. The liquid blown out from the broken pipes and the gas release valve, and glass fragments were scattered within a radius of ten meters. There was no injury. The analysis of the incident (Wada et al., ICHS 2007) assumed as probable initiating cause that titanium electrode in the electrolysis cell was exposed to oxygen and burned. Another possible co-cause is that that the generated hydrogen ignited. Consequently, the hydrogen-carrying water flow mixed with the oxygen-carrying water and ended into the oxygen separation tank, producing an explosive mixture and causing an explosion breaking open the pipes. The voltage to the generator was shut down in an early phase of the incident. Later on, also the water recirculation pump was shutdown. Nevertheless, the pressure inside the cell kept raising from a nominal value of 40 MPa to a value estimated around 100 MPa, despite the activation of the safety valve.
Event Date
December 7, 2005
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Causes
Cause Comments
The immediate cause, probably the reaction between oxygen and the titan electrode, was a probable consequence of a ill-design (unknown behavior of materials under high pressure oxygen) and a lack of risk assessment.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
high pressure electrolyzer; titan electrode; oxygen separation tank;
Storage/Process Medium
Location Type
Location description
Inhabited Area
Pre-event Summary
Although not clearly stated in the event source, it appears that the event occurred when 'verifying' (prototype testing?) the high pressure electrolyzer at a university campus.
Currency
Lessons Learned
Lessons Learned
Lessons Learned as reported in the article of Wada et al. (ICHS 2007, original English text partially modified): Risk assessment on test operation: Risk assessment should be done to know the risk of the operation and to take safety measures even if the operation is under testing or temporary. High pressure oxygen can burn metals: Under high pressure oxygen, metals could burn. If equipment in contact with oxygen, it should be made of material the behaviour of which is known at the expected operating conditions. Pressure rises at the closed end of pipe: If pressure wave happens in a pipe, it may cause excessive pressure than the strength of the pipe at the closed end of pipe and it will burst. Safety management system at research institutes: Institutes, including university, should organize the safety management system, even if they do only test or temporary operations.
Event Nature
Emergency Action
During the progress of the run away reactions, measures were taken, such as the shut down of the electrolyzers and the circulation pump, which however did not prevent the explosion.
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Orignal source is RISCAD. This case was also presented at the ICHS 2007 as example of RISCAD content:
Y. Wada, et al. http://conference.ing.unipi.it/ichs2007/fileadmin/user_upload/PAP_ICHS0…