Scientists from the HySA Infrastructure CoC in South Africa and the All-Russian Research Institute for Nuclear Power Plants Operation have determined how hydrogen behaves during an accidental leak from a small benchtop electrolyzer. This issue is becoming increasingly relevant, since compact units for producing green hydrogen are being used not only in industry but also in scientific laboratories, with the potential for household applications, which means that the prevention of the dangerous accumulation of oxyhydrogen in confined spaces is critical from the viewpoint of safety.
In their study, the researchers simulated an emergency situation caused by the depressurization of a hydrogen line inside an electrolyzer housing. They reviewed four scenarios with leak pressures ranging from 1 to 6 bar and assessed the effectiveness of simple forced ventilation with an airflow rate of approximately 1 meter per second.
The study combined experiments and numerical modeling.
During real-world tests, hydrogen concentrations were recorded by sensors that were installed under the housing cover, where this gas is most likely to accumulate due to its lightness. At the same time, computer modeling was conducted with STAR-CCM+ software, which provided a three-dimensional picture of hydrogen distribution throughout the entire interior of the device, including tubes, separators, desiccants and other components.
The researchers found that without ventilation hydrogen, which is almost 15 times lighter than air, rapidly rose and accumulated near the housing ceiling. Concentration reached 8–9% at a pressure as low as 1 bar, rising to 23–25% at 6 bar. This considerably exceeds hydrogen’s lower flammable limit in air (about 4%), which means that at these values, even the smallest ignition source could cause an explosive situation.
Calculations showed that the highest concentrations form in the compartment where electrolysis occurs, whereas gas penetration into the electronics compartment is reduced due to the structural separation.
Moreover, even moderate forced ventilation brings about major changes: with leaks under 1–2 bar pressure, hydrogen concentration drops to tenths of a percent, which is a safe level; at 6 bar pressure, ventilation maintains the concentration within 3–5%, limiting the volume of a potentially flammable mixture and preventing hydrogen from entering the compartment with electrical system components.
The numerical model also made it possible to identify potentially vulnerable areas: for instance, a localized stagnant area can form in the far corner of the housing behind the hydrogen separator, where gas lingers longer than in the rest of the electrolyzer. It is recommended to take these areas into consideration when placing sensors to ensure the early leak detection system is activated as quickly as possible.
In the future, the researchers plan to analyze other leak scenarios and gas outlet geometries, evaluate various sensor placement schemes and ventilation configurations and expand the set of modeling scenarios to develop practical recommendations for designing safer compact hydrogen plants.
