The battery manufacturer Corvus has presented its preliminary findings after the fire onboard the ferry Ytterøyningen this fall. The Norwegian Maritime Authority (NMA) said it backs the findings, even though the NMA also would like to consider a report from Norwegian police drawing its conclusion.

According to Corvus’ preliminary findings, the cause of the initial fire was most likely a leak from the cooling water system of the battery pack. Findings indicate that a twisted gasket in the cooling system most likely caused the leak. It has not yet been determined what caused the twisted gasket.

Due to the ongoing service work, no part the battery system was connected to the ship systems at the time of the incident. Consequently, no alarms from the battery system were sent to the ships alarm system.

Like others that have looked at the incident, the NMA stated that it has also focused on finding out why the incident escalated and resulted in an explosion several hours after the fire had been extinguished.

According to the NMA, the escalation of the incident may be connected to the use of the seawater sprinkler system for a short period of time, which among other things, caused several short circuits.

Corvus Energy CEO Geir Bjørkeli described the fire as a one-off event in a press release.

“For Corvus it is important to release the preliminary conclusions on the cause of the fire on board Ytterøyningen, thus avoiding speculation and uncertainty regarding the safety of lithium-ion battery-based energy storage systems. Safety has been, is and will always be Corvus Energy’s first priority,” Bjørkeli said.

The company underscored that its preliminary findings were supported by all parties involved in the investigation, including Norwegian Maritime Authorities and DNV-GL.

The investigation has been led by the Kvinnherad police in Hordaland, Norway. Fire engineering expertise from the Norwegian National Criminal Investigation Service, DNV GL, Norwegian Maritime Authorities, Corvus Energy, insurance companies, and other stakeholders have also been involved.

The car ferry, built in 2006 and converted to battery-hybrid in 2019, was in regular operation, running on its diesel engines when the fire started. There were twelve passengers and three crew members aboard the vessel at the time. The vessel was able to moor safely, and all passengers and vehicles disembarked as scheduled. No personal injuries were suffered in connection with the incident and no environmental damage has been reported.

Based on the investigations aboard the vessel, supported by external experiments and analysis – Corvus said that the following preliminary conclusion has been made:

The most probable cause of the fire was a leakage in the battery system’s liquid cooling circuit. Findings indicate that a twisted gasket, intended to seal the cooling plate outside of a battery module is the most probable cause of the leakage.

It is too early to conclude whether the twisted gasket was a result of the recent service work on the cooling system or if it was caused by other reasons.

The leakage created arching between electrical components, at pack voltages of 1000Vdc, igniting a fire. The fire was fueled by ethylene glycol components from the coolant and caused external heating of battery modules.

Due to the ongoing service work, no part of the battery system was connected to the shipside systems at the time of the incident. Consequently, no alarms from the battery system were sent through the ships alarm system.

Findings have shown that the patented and certified Corvus Passive Single Cell Thermal Runaway isolation safety system has worked as designed and intended, most likely limiting the damage from the fire.

Both the vessels Novec 1230 inert gas system and the vessel saltwater fire sprinkler system were deployed during the event. The saltwater sprinkler system was installed as an additional safety barrier. Indications are that the activation of the saltwater sprinkler system contributed to escalating the incident.

The further investigation will focus on how the extent and severity of the following events were able to develop towards an explosion 12 hours later in the switchboard room adjacent to the battery room.