An assembly error of a specific plug in a hydrogen tank in the high-pressure storage unit has been identified as the root cause of an explosion to a hydrogen station in Norway.

Nel ASA has been investigating the incident at the Kjørbo hydrogen station, located just outside of Oslo, with safety consultancy Gexcon and released the latest update today.

The preliminary Gexcon investigation shows that the incident started with a hydrogen leak from a plug in one of the tanks in the high-pressure storage unit.

This leak created a mixture of hydrogen and air that ignited. The investigations will continue into the specific source of ignition.

“Based on our investigations and analysis, we can conclude that the leak started in a specific plug assembly in one of the tanks of the high-pressure storage unit,” said Geirmund Vislie, Vice-President Consulting of Gexcon.

“We will continue the investigations to understand the possible mechanisms of ignition.”

Together with the authorities, Nel and Gexcon have finalised the off-site examination of the high-pressure storage unit.

With the root cause now identified, Nel will conduct an inspection and integrity verification programme for the high-pressure storage units with similar plugs.

Additionally, Nel has initiated a programme outlining new assembly, verification, and documentation procedures.

Previous generation stations, as well as US and Korea stations, have a different concept and design for the high-pressure storage units. As such, a leakage of the kind experienced at Kjørbo cannot occur at these stations.

“We deeply apologise to those directly and indirectly affected by the incident,” said Jon André Løkke, CEO of Nel.

“Nel has an unwavering ambition: No incidents at sites with our technology. We take this extremely seriously and have deployed our full resources to resolve the situation.”

“With the root cause now identified, we are implementing measures to prevent this ever happening again.”

“Further, we’re happy that the Nel core technologies were not the cause of the leak, and that the fuelling stations with different high-pressure storage designs can be reopened soon.”